5'8 prob go for a medium, try a men's and women's specific, working in a bike shop i find that not every woman get's on with women's specific geometry, don't go for miles and miles of suspension, 4" should be ok, or 5 if you want to chuck it around a bit more.
dual suspension is more maitenance than a hardtail, but as long as the bike is kept clean, i.e. wash after every off road ride then you should be ok.
if you want to learn to ride properly go for a hardtail, also easier to ride to from work.
also go for a multitool, not just a spoke key, and tbh trueing wheels can be hard to start with, so it's worth getting someone to show you how.
also your budget will also dictate whether or not to go for full sus or a hardtail. hope this helps