You could definitely do it. Also, a good thing to link up with it would be Day Job, which would give you rules to govern how much time and money is involved. At 40 hours a week, you make 5000 a month, which would make it a lot more reasonable to make 3 successes and break even, or the occasional good or bad month where an extra grand gets thrown into the mix.
Alternatively, you can modify the Trust Fund lifestyle and use that to pay for a modified commercial space, using the bonus 2000 from the High lifestyle allotted rent to cover adding a Low quality upstairs apartment, or moving the comforts and necessities up a bunch to allow the room at the back to run a functioning house.
I am more in line with using the Trust Fund because it is a positive quality, and therefore should you ever get busted, you don't owe 40 hours a week to community service or arguing your legal right to work until you pay 30 karma (yeah, seems like a GREAT idea to buy up negatives, until you have to pay the piper... That right there is 4 specializations, or a level 6 skill, or hard-capping an attribute) but rather just sacrifice your store and income and get the hell out of dodge.
If you tack on Black Market Pipeline to either of those, it also gives you an awesome front to bring in items useful to the store and to you, and reasonable grounds to sell stolen goods at a better value. If your contact is a corporate man, extraterritoriality agreements could make those goods totally legal where they end up.
This all reflects my preference to use existing rules in creative ways to represent a character trait. I would always rather interpret a rule to apply instead of making house rules, because they are usually less arguable and fit into game balance more predictably.