Evaluating a "co-founder" offer

I was presented with the following offer and while I'm waiting legal advice, I'm interested to know your opinions.

I'm been offered a "co-founder" seat with a bit over 10% in stock options vested over 4 years. This is bit unsual arrangement due to the fact that I'll be doing this as my side project for the first half year. Idea is to get revenue/funding so that I'll can start work fulltime with salary after that. Currently the company is doing it's first steps with no real customers(excluding FFF) or working product.

I would like to know how to evaluate this offer? Is there any terms that I should include?

You have to look at a few things:

1. Option vesting is fine but what is the price for the stock when or if you decide to exercise them?
2. What if any revenue sharing will be offered once you go do this full time?
3. How will the options vest? 25, 50, 75, 100 or in some other manner.
4. What will happen if the company goes under? Are you as co founder be responsible for full or partially reimbursing the investors (probably not, but stranger things have happened)?
5. What are your responsibilities as a co-founder?

I am sure there are more points but I can't think of any at the moment.