Typically, when changing a house to commercial use, you should expect to rebuild any EXTERIOR entry stairs and/or porches. Existing houses usually have a change of level at the entry door threshold and entry stairs that are too steep an uneven to meet current commercial code.
You may need new/additional handrails at any INTERIOR stairs, but the slope of interior stairs is generally exempt from review in a change of occupancy.
For the typical house, a single exit will usually be okay, even when the basement or second floor will be used commercially. For large houses, the increased exit distance may mean a second exit.
For a basement to be converted to commercial use, the code requires 7' 6" of ceiling height (though there may be a few inches of wiggle room, via a simple appeal process). If the basement would be used only for storage, 7' 0" of headroom should be okay.