That is a really good opening post, quite a bit of useful info in there. Te right FS bike has basically reached a point where there is almost zero downside other than weight because pedal bob and brake jacking is minimized... but they cost more than a hardtail bike. I you can afford/justify a good FS bike, do it. However, if you are spending less than some certain amount it often becomes better to get a HT bike than FS due to suspension design and components.

Here's a few quick hits to think about:
- at 5'7.5" you are on the edge, by some opinions, of riding a 29er. I would strongly consider 26". I'm building a 26" FS bike right now, and I'm 6'0".
- the US is going 29er crazy and you can often find good deals on 26".

- ask about vendor- or bike shop-sponsored demo days or bike rentals. MTB rentals can be quite expensive, because the bikes can get some considerable wear & tear, but it helps to buy the right bike. I'm talking about riding on trails. demoing a MTB in a parking lot is very low value.
- you can also ask around who has a given bike and ask them about it, or maybe even ride it. personally, I wouldn't ask a stranger unless they offered a demo ride.

- the fork is the most critical piece of equipment on a suspension bike. try some bikes with cheap, mid-priced and higher end forks to see the differences.