How big is your basement and how big a frame do you plan to get? Definitely do as Glassquilt suggests by researching taxes issues regarding business vs personal use. There is a difference.
Also, agree with figuring out cost of construction vs remodeling the basement as well as heating and cooling costs before doing anything.
We just moved from a condo(1200 sq ft) to a house(2475+ sq ft). The house has a formal DR/LR that we will never use, so DH had me move in there to use as my studio, and I was finally able to get a LA w/12 ft frame (yeah, no longer have to rent one). We do have a family room and eating area.