First of all welcome.

Generally, receivers from the same company will match pretty close. If you get and upper and lower from separate companies, their finishes will not usually match. Which companies did you go with? This is not a big deal, unless you are a little OCD (we all are) and want them to match perfectly. This doesn't affect the function of your gun.

A stainless barrel will easily do what you want it to do at 200 yards or less. In fact, I'd probably go 16" with a 1/8 twist. At 200 yards, you won't miss the extra velocity with a 16 vs 18. I'm sure some of our regular hunters will chime in.