What terms should be better to set when creating a Startup with your PhD supervisor?
I strongly suggest that you hire a lawyer to get this advice. Failing to do so could lead to a huge amount of conflict later. It is likely that your interests don't completely align with those of your advisor.
I'm not a lawyer so can't help much, but it might be possible to set up a joint meeting with a lawyer and the advisor to work out an equitable arrangement. Your joint venture will need legal advice in any case.
But you also need to consider what a conflict would mean for finishing your degree. Don't put that in jeopardy.