Specialized Tricross Sale

Right,

I was thinking about building a single speed bike but stumbled across this bike. I could do with one pretty sharpish for work and note that Pearson's have one in my size (I am 6ft 1, so 58cm I reckon). I am new to the whole ss world having only ever ridden geared bikes in the past, so a couple of daft questions first up.

1. This isnt fixed, simply single speed, so I can free wheel in it?
   
2. I will be able to upgrade it easily as I get used to the set up?
   
3. The frame/wheels will take my 14.5stone weight? The reason I ask this is that a mate of mine had a decent geared bike but he was a big lad and used to complain about his wheels/frame not being strong enough for his weight - this might all be bullsh*t but I reckoned it was better off asking a stupid question than just being ignorant.
   
   

I am still not sure if I will go for this bike rather than building my own, the satisfaction of building one may prove to be too strong...