If you're looking for a budget full-suspension bike, that Yukon FX you posted is pretty highly regarded in that category. However, if you're looking at riding fire roads and gravel trails, you may be better served with a hardtail, since you'll end up with better components for the money. On the other hand, if you think you'll eventually end up on technical singletrack, it might be worth it to go FS.

Since you're talking about fire roads and gravel trails, and you're describing yourself as a roadie, I'd look at cross-country bikes. They'll have geometry more suited for speed and will be a little lighter than a trail or all-mountain bike.

At 5'2, you will almost definitely want a small, perhaps even an extra-small. Try the bike before you buy it. I'm 5'3, and some smalls are way too big...I test rode a small Specialized Enduro and small Ibis Mojo and both were too big. I also had a short Norco One25 for a little while that I sold off because it was too big and felt like a bus in the air. My full-suspension is an XS and my hardtail is a small, so sizing will vary from company to company.

29ers feel like monster trucks to me. I'm not sure if it's because of my height or riding style (or both), but they're just too unwieldy. They may actually be ideal for the riding you're describing, but tiny frames on big wheels make for some strange geometry. Again, try before you buy.