it all depends what is he contributing.. You said that you believe "he can contribute a lot in many areas that need to be covered in order to build a succesful app company", but what is it exactly? Who's coding the app? You've already done first app, if he's contributing to marketing of the first app then he can get less than 30% of profits from that app. If you've already built second one, the same thing. If he's building the second app with you and brings more skill you might consider splitting evenly just for the second app, you don't have to give away equity within the company, you can make an agreement to split profits just for the second app, since he can decide to leave.
you can start with your true goals right away, in Elon's example he wouldn't be able to start building Spaceships without having billions on dollars in his pocket... If the true goal/passion requires less capital and you have it available then go for it right away
It seems like Elon Musk did exactly what you just described.. He sold his first 2 startups and now he's real passionate about things he loves: physics and anything that has to do with it (space, cars etc) . Once there's unlimited resource it's easy to do things you want