You should be fine with just a bolt alone and maybe the enhanced firing pin kit.
The barrel extension should have one feed ramp instead of two, if not you may have to dremel it out for reliable feeding. 7.62 is also known for weak cycling from standard AR gas systems so a larger gas port may be needed. Some folks swear by the dedicated 7.62 mags but if all of the above checks out standard mags should work.
Lots of info out there on this subject. You can also buy a complete 7.62 upper from a reliable source and be good to go.
I think you're mixing some good info with bad, and I'm guessing you're thinking of a different cartridge than 7.62x39.
Just a bolt to go with that barrel is fine, don't need to change the entire BCG.
One feed ramp? No, two feed ramps is still correct. You may have a barrel where the feed ramps are blended together into one, but that's not necessary for this caliber. Maybe you're thinking of the big stuff like 450 Bushmaster that is single feed.
And yes, you absolutely do need specific 7.62x39 magazines. That cartridge does not work reliably in 5.56 mags. Again, you're probably thinking of some of the bigger cartridges that work as single feed in 5.56 mags; that is not the case with 7.62x39.
Also Boss .300 Winmag - the barrel doesn't have to be from the same manufacturer. If it's for a standard AR15 from any manufacturer, it should fit yours. Part of the appeal of these rifles is that they're modular that way.
