I mostly was referring to having your partner cosign or put up some assets himself, instead of you taking it all on yourself. Honestly, though, a lot can happen in 3 months. Be careful not to get in over your head and get yourself in a position where you're subject to financial hardship if something goes wrong. Of course, a 10K loan isn't really that much, and split two ways, it could be paid off inside of a year without too much trouble, so it doesn't seem to me like your risk is too high.

That said, you might want to take a little bit more just to give yourselves some leeway. That would allow you to use a portion of the loan to make the initial few (6 or so?) payments. If you think you're going to need to support your partner for 3 months full-time, I'd shoot more for 4, and allowing yourself a full-time month (in case it becomes necessary) might not be bad, either. Finally, I'd suggest using some of it for the operating costs you mentioned, so that you can work your other job a little less and spend more time on the startup.

One last suggestion: sit down for some time with your partner and discuss what the loan will need to pay for, how much is needed, and how it is going to be allocated. Leave part of it unallocated as a contingency fund. Discuss how to split the responsibility for the debt in the event of a failure. In other words, get everything on the table now so that there are no surprises down the line.