There are no hard and fast rules.
But some guidelines.
The first priority is to make sure that employees get paid fairly for the work they put in. So all other things being equal, you should get a full salary for what you do and he should get a part-time salary.
After that there should be a return on the capital employed. If it's very risky, you would expect a higher return. If you are investing a lot, then you will want most of the profits.
Given that it's your idea, that you will be working full-time and that you will be providing most of the capital, I think you should be aiming for 100% of the shareholding and profits.
You can thank him for his input by maybe paying him well for his part-time job. Or you can offer him shares in the business cheaply.