I have a completely stock 2000 C5 auto with 20,000 miles. My plan is to likely keep it for 20+ years (no--I'm not kidding). I only drive it about 30-75 miles per week, mostly over the weekend. I just bought the car over the summer, but once spring rolls around (I'm in PA--too much salt in the winter to drive it), I may drive it to work 1-2 days per week, which means I'll probably be putting 100 miles per week on it from March-November...so total mileage of about 4,500 miles per year roughly. I am looking for good gas mileage (currently around 27 mpg with stock 2.73s) and same reliability (or similar) to what it is now. So, I am debating putting a few thousand into it for performance mods. My goal is roughly 430-450 very reliable, not going to kill the engine, transmission, or differential, crank horsepower. My options are either:
A.) East Coast Supercharger kit with restrictor plate at about 5 psi, which should be 450 crank hp (or so I'm told) and Corsa Xtreme axle back exhaust

B.) Combination of long tube headers, FAST intake, Callaway Honker, upgraded throttle body, Corsa Xtreme axle back exhaust (I'm thinking all these modifications should get me to 415 hp at the crank (?)) for slightly less than the supercharger from ECS...and maybe, a mild cam for ~25 more crank hp

The thing is, I am completely undecided, and in all honesty, don't know all the advantages and disadvantages of both. I love the idea of the supercharger, but I'm told my block has a 2 bolt main vs later LS1 Corvettes with a 4 bolt main, which may kill the engine with a supercharger. Any truth to that? What is a 2 bolt main vs 4 bolt main and which does my Corvette have vs other C5 Corvettes? I'd like to keep all modifications to $7,000 or less, with a goal of low, low 12s or 11.9 if possible (not going to drag race it--just saying how fast I'd want it to go as I think C6 autos from 2005-2007 run low-mid 12s and I want it a bit faster). I'm open to any and all ideas and suggestions as I'm far from an expert on this. Any advice would be very much appreciated.

Either one will be an easy solution to your wants/needs.

Pro's:

Supercharger:
Less stressful on the motor when not hard on the throttle
Can get away without buying air intake, headers, axle back exhaust, etc and still probably make near 400 RWHP at 5-7 PSI.

Head/Cam setup:
Larger powerband
No supercharger belt issues/maintenance

Cons though:

Supercharger
Cost. It's gonna be expensive
Maintenance
Belt Issues (slip, alignment, etc)
Harder on motor if you put your foot in the gas a lot
Beginning stages of a sickness called mod fever.

Heads/Cam
Loss of driveability/fuel economy
cam will increase idle/exhaust noise
depending on cam increased valvetrain wear
Will get pricey quick after heads/cam/headers/exhaust/intake
See above for mod fever.

Sounds like he has mod fever already with a budget of 7k! lol
Finding a used blower set up and camming the car with a clutch upgrade, is the way to go, I think. Otherwise, a turbo car would be insane. That being said, I think a cammed set up with a good tune will probably be safer for your 20+ year ownership goals.

If I go N/A route, with some sort of combination of long tube headers, exhaust, cold air intake, etc, and if I added a cam to that setup, which cam numbers would be good for 20-25 crank hp with minimal wear and tear on the engine? I would love a cam, but I'm told depending on the cam type (the numbers--for instance--112 vs 119 vs (insert number here), some cause a lot more wear and tear and I'm looking for the safest route possible (least destructive on the longetivity of the motor--even if that means sacrificing some power. So, which cam numbers (I'm not sure of the formal name for "numbers"--but I know you know what I mean haha) might be good for a mild cam able to add 20-25 hp in addition to other mods while not hurting/damaging the motor?

Wear and tear from a cam is dictated by the lobe profiles, lift, ramp rate, etc. Bear in mind that PLENTY of cars put medium sized cams in and live long happy lives. Others, not so much. It's part of the game you play when modifying a car.

I think if you went with GOOD headers, meaning LG, Kooks, or American Racing (just my opinion), a solid CAI like a Vararam or Callaway Honker, and something like a TSP224R cam kit, and a set of ported LS6 heads, you'd make about 400 RWHP with a VERY tame setup without a bunch of headaches and not having to sacrifice much at all.

I think the supercharger route would be the best.. that is what I'm looking forward to doing. During most of my research, it seems to have the most promise IMHO.

That could work. How much (estimate--not exact) are new ported LS6 heads? I know cams generally run $250-$400 or so, so how much for heads and cam install at an "average" performance shop? Maybe $2,000 for install of heads and cam (not including the actual cost of the parts)?

My cam build (no heads) cost me about 2500 including the rods, springs, cam, timing chain, oil, and labor.
Figure another 500-600 ish worth of parts/labor if you're doing the head also once the motor is opened up.

So if I do the cam, it's only another $500-$600 (approximate) for heads (parts) and head install (labor)? Really?! That doesn't seem bad. I was really thinking supercharger, but now I'm thinking heads and cam. Does a mild cam and heads upgrade really hurt mpg?

How much maintenance does a supercharge normally require other than the fluid change which, from what I understand, should be done on the same cycle as oil changes?

Since you have an auto trans your also gonna need a different torque converter and a different rear diff. if you go F/I and remember Cheap Fast Reliable pick 2 you can't have all 3

Will I definitely need torque convertor and rear diff. if I go F/I or it's just suggested? I'm having trouble deciding all this because of exactly what you said...I want cheap, fast, and reliable, but I know it doesn't work like that. I guess you could say I'm looking at reliable and fast, with a total modification budget of $6,000-$7,000 over the next year. Once I run through $6,000-$7,000 I'm done with spending, except for maintenance and general wear and tear.

Look at it like this, the blower set up is going to be 5K alone.. Then there is heads a cam all the gaskets and much more depending on your goals

If you kept the cam small so as to not lose the bottom end of the powerband, you could get away without a torque converter and diff. Frankly, for what you're going to be using the car for, I'd put those well on the back burner. They'll both pep the car up some, but remember if you put a torque converter in then out of lockup it's going to want to flash to it's stall speed as you're driving around, and that will impact driveability and economy.

Personally I like the supercharger route. I put a D1sc procharger on my completely stock 03 has 8 psi boost and a safe tune dyno was 510 RWHP and is completely the same car until I nail the pedal. No need to change transmission, gears, torque converter. It's not the cheapest route but pound for pound is the best power mod in my opinion. My buddy went the other way and did cam headers and intake and he has remorse he didn't go FI haven't had it to the track yet but should run very low 11 maybe even clip at high 10 in real good air at sea level.

Thanks. Because your C5 is a 2003 and one is 2000, does that mean I have a 2 bolt main and you have a 4 bolt main? I'm considering a supercharger but I've heard about this 2 bolt main vs 4 bolt main (I'm not even sure what it means, though?) and how a 2000 Corvette can't safely run a supercharger because of it's 2 bolt main? I just don't want to destroy the otherwise perfect motor.

I believe and I'm sure if I'm wrong someone will correct me quickly lol all LS engines are actually 6 bolt main blocks that means there are 4 bolts on the main caps plus 2 side drilled for additional strength. There are great sources on this site to discuss superchargers in depth east coast superchargers are an excellent source and he can answer any question you have and I've seen several 2000 c5 with superchargers pushing way more HP and boost than I am. On a side note the first time you crack that throttle with a supercharger the smile is worth every penny. Best mod I've ever done

Over the summer I did long tubes, catted X, rebuilt and ported 243s and a mild (perhaps baby) cam 222/226/.600/112 cam (also, trunnions, lifters, oil pump and timing chain). I already had the cold air and ti exhaust. Just over 400 at the wheels so 450+/- at the motor. TQ peaked at 380 but improved all across the curve. Stock driving manners (I have a 6m) and it pulls all the way to the 6,750 limiter. I did this all way under your budget and did not do the labor myself.

Having said all that - superchargers rock too!

Supercharger. I'd look at the new Magneson 6th gen series.
Full boost at low rpm, has a turbo personality compared to the ECS/A&A.

Ok, before you start doing mods, based off of this, I'd STRONGLY suggest researching the platform and learning about the motor. ALL LS motors are six bolt main setups, four straight vertical and two in from the sides. You're referencing the Gen 1 and 2 architecture which is totally irrelevant to the LS motor family. Do some reading, educate yourself, then make your decisions.