The IRO wheels have received fairly good reviews on here. The consensus is that if you set them up right, they will treat you well. If you buy just the hubs and build them up yourself you can save money on shipping.

You find out what spacing you need for the rear hub by measuring the distance between the rear dropouts. It will probably be from 125mm to 135mm.

I've got no experience with IRO's other parts. From what I can infer, they are pretty standard quality generic parts. Probably won't fall apart on you, but certainly not high-end.

As far as parts fitting on a track bike later, that all depends on a number of factors. Most track bikes have 120mm rear spacing, so if you get a 120mm hub and use axle spacers, that should help. Crank compatibility depends on BB. Stem compatibility depends on the headset, headset compatability depends on the fork, etc.

In my experience, the only things that I can count on to go between to bikes are the saddle, front wheel, and pedals. Even pedals can be a wash, if the cranks have french threading. But, if you know what you are doing when you switch over, everything can probably be kept.