I'm currently at 270 but have rode at 290, way more then 300 with camel back and stuff. As for rear suspension you won't have much luck with a coil spring, but maybe you could find one. If you go full suspension go air. I had zero problems with 3 different fox rear shocks pumped up to 270-290, their
limit is 300 lbs pressure. I'd say it would handle you.
Lockout is kind of nice, that is when I remember to use it. Great for the fireroad climbs, but I could easily go without it.
I've broke 2 of the 4 full suspensions I've owned and 1 of the of the 3 hardtails. If your trails are rough your gonna break frames. Have a warranty.
Everyone that tells you that good full suspension is expensive knows what they are talking about. Cheap full suspension is usally more trouble then its worth.
I ride my full suspension more then my hard tail, but mainly because my hardtail has a steep head angle and feels sketchy. I think the full suspension will wear me out faster then the hard tail, but the hard tail has litterly rattled a filling out.
Hard tail is probably the better choice. Full suspension is much more fun when going fast and decending. Hard tail is more fun everywhere else.