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Keep the stock plugs. Unless and until you install a blower or a big shot (125+HP) of nitrous, you're not going to find a plug that works any better, IMHO.
On the 160 degree stat you're gonna get mixed advice. I have one in mine and with the fan settings I have now the engine coolant temps still run in the 190s. You don't need to change that either though.
Best thing to do is to just install the headers and x-pipe for now and get it tuned for those and you'll be pleasantly surprised with the outcome.
BTW: What kind of headers are you doing?
Run the ACDelco iridium plugs. They provide great spark, for stock applications and last 100,000 miles. I usually check them around 50,000-60,000 miles. I always changed mine earlier if needed. Never one issue with these plugs. As goes for the spark plug wires. I gained no performance on the dyno with Msd and put the stock ones back on cause the boots were cracking. As for the stat, if you run a 160 you should have the fans tuned to turn on earlier. When I put on my supercharger ( in my C6 ) I was told to leave the stock stat in. I would put in an oil cooler before a lower stat, but that's my opinion. Since your putting on headers and x-pipe I would assume your getting a tune? The norm for a tuner is to turn the fans to come on earlier. You will get a cooler motor and notice more of a difference running a true cold air intake, such as a Vararam. Some here will say Vararam sucks, this one's better etc... If you decide to run a cai it needs to pull air from the front of the car out of the radiator bay.