If you have to ask that question then you must have all the disposable time and money but absolutely no passion or experience. The real answer is build somethi

If you have to ask that question then you must have all the disposable time and money but absolutely no passion or experience. The real answer is build something you know obsessively well, are extremely passionate about, and something that is vaguely original. If you can't do that don't do a start up. If you just have that much time and money to throw away fund a popular (existing) open source software project into a commercial enterprise.