Thank you all for the comments and for the great advises.
As you probably have guessed, based on the fact that I posted this question here, I didn't fell comfortable giving up 50% (49%, to be correct) at this stage.
The whole process can be paused, and to answer to Richard - there is no real shelf life. What I mean is that, as any idea and product, if it is not executed and placed in the hands of the customers, it will eventually die, but other than that, I can spend some time to find alternatives.
In fact, my advisor said I need to slow down and be very careful with such partnerships. His advise was very much like Orion's and Richard's.
I think I will work on a performance based schedule. I plan to offer them 1) commissions and 2) tie the equity to revenue (discounted). I will expect results with no investment done from me in advertising.
This will help me verify their capabilities and also see if in fact, we can work together.
I hear the range of 5-20% very often, from different people with different backgrounds. May be that is the range I should be considering.
Any examples or links to help me develop a schedule (connecting sales performance and equity) would be appreciated.
Thanks again to all of you, it is amazing that I can reach for help to so many experienced people :).