Need assistance on dressing my new 870

[Synchronizor]

Then some mandatory (in my opinion for my circumstance) internals being the firing pin, extractor and extractor spring.

I know the machined extractor is a popular "upgrade" (personally, I think the MIM parts are superior), but why are you changing the firing pin and extractor spring? Are yours worn?

one question I got is will I need some sort of brace for the mag extension to the barrel?

You don't need to clamp single-piece extensions like the Wilson Combat, especially if the barrel you're buying has a locking detent in the guide ring, but you can still use a reinforcing clamp or bracket if you want to make your build as durable as possible.

[CynicZ]

my firing pin and extractor spring arent worn but with it being a 10yr old gun (guessing from wear and tear and such) why not spend 11$ to replace them while im breaking it down giving her a good cleaning.

[Synchronizor]

It can't hurt to change out some springs when building on a used shotgun, but the firing pins in 870s are a pain to take out and replace. If there's no visible damage to your current one, it may not be worth the hassle.