>>277036391. If you want a faux buffer tube, the VLTOR ones are pretty good. Put your stock of choice on.
2. Look it up, it's easy. Honestly though, the default AK lower handguards are godtier for holding onto. Quadhandguards are uncomfy, and a compromise towards loading a rifle up with a lot of military foreend stuff.
3. Russian, no Korean or US drums need apply. Drums are kinda gay on semi AKs though.
4. No, you can do it yourself if you are even a little bit mechanically inclined. The default sights are honestly fine; try them out a little bit and come with an open mind before trying to modify all yer shit. Also, aftermarket irons are better, but not by much, if you aren't getting an optic, I wouldn't even bother with such moderate replacements, especially considering the cost of replacement irons rivals the cost of mid-tier optics.
TLDR: Before you go nuts upgrading all your shit shoot it stock for a while and really try to enjoy & get good with stock before dumping a ton of cash into it.