After we cover both of our salaries, what type of work/life balance do you want?

The reason I think this is important, is the start is always a grind. But, when you get to the stage of going full-time, worst feeling is when one side thinks they are contributing more. Being aligned on expectations from the start will save lots of headaches in the future.

Another question, which I think you need to ask yourself, is if you would enjoy working with that person. Going with a cofounder means you're going to be spending a lot of time together. They could be the best in their field, but if they are insufferable, it's not worth the headache.