Simple question: Does the studs have to be against the wall? CAn I put in a few inches gap between the concrete wall and the studs?
Yes you can put a gap between the wall and the studs. Some people do this so they can glue in Rigid foam insulation to the basement walls.
I would recommend a gap of an inch or so as it provides some airflow behind the wall. Since foundation walls are rarely straight moving the framing away from the foundation allows you to make your walls straight and plumb.
If they are against the wakl below grade they also need to be pressure treated.
Use a pressure treated bottonm plate and hold the studs off the wall at least an inch.
"pressure treated bottom plate"
You can also use a half or one inch thick piece of Styrofoam under the plate or polyethylene sheeeting. The interior of the wall should also be dampproofed, but only to the grade level. (Board-type insulation, preferably with taped joints and sealed at the bottom and top, does the same job.)
I have been using non-structural steel framing in basements lately. It's less sensitive to water and doesn't support mould growth. It doesn't add moisture to the air nor shrink and cause screw pops later. It's also much easier to bring in, work with (no sawdust in a confined space!) and clean up.
Used metal studs for my entire finished basement - 2200 sqft. Like Worthy said -easy to carry in and work with and very easy to cut and clean up. It does help to have a brother in law in the commercial carpentry business for tools and help though.
Are metals studs more expensive then wood studs?