SKS for hunting...
Sureshot--Firstly, while the 7.62x39 CAN be used for moose, deer, bear, and coyotes, there are better cartridges to be had for each one.
For moose and bear, especially, I'd want a cartridge with a little more oomph. There are lots to choose from: 6.5x55 Swede, 8mmJS Mauser, .30-'06, .308 Win, or 7.62x54R quickly come to mind, and there are lots more, on up through the various magnum cartridges. Of the above, the Swede would work the best for coyotes, and the Swedes themselves routinely use it on moose.
Secondly, as to your purchasing the rifle: $200 is a good price in my neck of the woods, currently, for an SKS in good condition. (Years ago they were about 85 bucks, but those days are gone forever!) A
Russian SKS or an Albanian, will set you back twice that; what you are buying is probably Chinese or Yugoslavian. The SKS is built like the proverbial brick pizzeria--It will work forever, and go bang every single time you pull the trigger. The Yugo SKS's barrel is NOT chrome-lined while all the others are, but this is only a consideration if you shoot cheap crappy surplus corrosive ammunition. (After shooting this you must clean your rifle right now, but if you do there is no problem.) And I NEVER recommend shooting cheap crappy surplus corrosive ammunition anyhow--there is a good reason it is so cheap!
Now the bad news: The accuracy of SKS rifles varies greatly with the individual rifle. Some are fine for "hunting accuracy," that is, about a 2" group or less at 100 yds. This is also dandy "battle rifle accuracy," which is for what the SKS was designed. However, you will find some SKS's that can't keep all their shots in an 8" circle at 100 yd, and obviously you wouldn't want to take such a weapon hunting and shoot it at a live creature. You can't guarantee a humane kill.
The only way to find out which level of accuracy is possessed by a given SKS is to take it to the range and try it out with several different brands of ammunition. If the seller will let you do that, and you find that THIS SKS is one of the "good ones," then well and good, buy it and use it for hunting. Otherwise I can't recommend it.
Thirdly you ask about bullet size. The SKS standardly eats 123 grain bullets, but it will take 150's OK. The 150's are probably a handloading proposition. If you handload already, no big deal there. Since the SKS is an autoloader, and one that is unusually hard on cases, you'll need to full-length resize every case every time, but you CAN re-use the cases (Given that they are brass, and Boxer-primed. Most of the cheap ammo is steel cases and/or Berdan primed--NOT a good reloading proposition!) If you don't handload you are stuck with what you can buy. 150 grain bullets MAY be available. You have to use softpoint bullets for hunting--The humane kill thing again, plus in most areas it's the law anyhow.
Frankly, if you are shopping for a primarily hunting rifle I'd keep looking. If you want a durable, inexpensive rifle you can plink with, and also use for hunting, and mebbe loan to your brother-in-law, then after shooting this one and finding that it is acceptably accurate, well, go for it.
Whatever you decide, please keep us posted, and we'll want pictures! Good luck in your search!