Hi David,
1. From observation, cafes have a lot of business during Summer because of tourists, but October - April seem to be quieter months and they need to be prepared for little income then.
2. To rent out any property in Gibraltar is quite expensive, while commercial property is rarely available. I would estimate the costs would be:
Rent £1000-£1900 per month (depending on size and location);
Rates £1000-£2000 per quarter;
Lease transfer (if applicable) from £20,000 to £100,000: one off payment;
You can see some current premises on the market here:
bfagib.com/commercials.asp
3. If they start in late spring months, depending on location they would probably make the ends meet in the first few months.
4. There are not many houses in Gibraltar - a comfortable one bedroom apartment would cost approx. £1200 per month plus bills (ca. £150)
I trust it sheds some lights on the issue, good luck!