what suspension fork should I get Thinking to get a Montague bike for mountain biking. The reason for a folder is easy storage and transportation. And reviews I read all say good things about their bikes. 
There are these models available:

http://www.montaguebikes.com/compare-mountain-folding-bikes.html

I have almost 0 knowledge on MTB, but based on my experience with other bikes, these frames are probably the same, only different components (except x50, which uses v brake so the frame/fork maybe different). So I am thinking to get the second least expensive paratrooper then buy a good fork later when needed. So what kind of fork can I put on this bike? Please let me know the points to consider (e.g travel, wheel size, etc etc remember I have almost 0 knowledge). I will be using this bike on off road, trails, etc but nothing too rough(jumping etc) in my mind. Or is the stock fork (SR Suntour. Suspension XCT V4. 80mm travel) already enough for my need?

BTW, I want to get a decent enough fork so I won't upgrade soon after that (at least I hope LoL). So the fork can be a little more than my needs.
It's a difficult question to answer as there are a lot of personal variables. 
"Nothing too rough in my mind" being the biggest variable.
For a lot of flat or rolling terrain without many obstacles; rock gardens, gnarly roots, etc, I would say the stock fork is fine. I have an old 26er with a similar fork which does fine on fast rolling trails but sometimes bottoms out on steep but abrupt drop ins.
However, to be honest, if I was worried about the fork being able to handle the terrain, I most likely wouldn't even consider riding a folding bike on it.