For the recalls the best I can suggest is to call a dealer and provide the VIN, they can give you a definitive answer.
Some had EPS some had hydraulic, I'm not sure what the deciding factors are. It's easy enough to pop the hood and see if there's a power steering reservoir/pump.
If it had EPS and it was bad, You'd see a "POWER STEERING" message in the DIC.
Some work like convertible or panoramic sunroof work may be turned away just because parts aren't available anymore.
They build the most G6s in Sedan form, and A LOT of parts are shared with the Malibu, Cobalt, Aura etc, Even newer buicks are built on a second gen version of the same platform as the G6.
Also the same platform is used for a lot of cars overseas like Vauxhall and Opel.
It's like any other GM product of this range, parts are mostly available and mostly affordable.
The G6 is also starting to fill up the junkyards, so second hand parts will be around for quite some time.
It does sound like it may need some work, especially in the suspension area. But without taking a look or going for a good test drive. it's hard to say for sure what you may run into.