You should expect to rebuild any EXTERIOR entry stairs and/or porches used to access the commercial function. 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 serving the commercial use, but the slope of interior stairs is generally exempt from review in a change of occupancy.
If the basement is to be used by the business, then the question of headroom would need to be addressed. The code requires 7' 6" of ceiling height (though there may be a few inches of wiggle room, via the appeal process). If the basement would be used for storage accessory to the business, and not otherwise used by employees or customers, then 7' 0" of headroom should be okay.