55/45 split
Any reason why you two don’t have the same equity ?
Inequalities in equity can go a long way, it’s commonly knowledge that unequal equities among founders can create resentment as time goes on and involvement changes.
Unequal equities are usually decided before getting serious when commitment is scarce, at that point sometimes the most active one can get more equity in the first 3-6 months.
However companies can take 4-5 years to takeoff, working you ass of for years and years can and will likely change the power structure among the founders. Unequal equity will then demotivate key founders as they’d feel robbed.
“It’s not really my project, I just need to get this done and after this one I’ll make my own company” is the root of all problems
Equal equities even if not ideal doesn’t create the same amount of resentement. For just 10% difference between you two, I’d suggest to avoid planting that seed for problems.
Question 1 and 4, indicate that you might need to really ask for help of an accountant or CPA.