I strongly recommend making your estimate fill the timeframe you specified, break that down into what salary you would want and then bill hourly, every two week

I strongly recommend making your estimate fill the timeframe you specified, break that down into what salary you would want and then bill hourly, every two weeks. Do not base it on milestones unless it is something you have built before and "could do it in your sleep" because otherwise you are going to trip on a bunch of "gotchas" and at some point either you or the client are going to be frustrated and/or forced to renegotiate.