First off, there is not enough information for a qualified expert to provide an expert opinion.

This is because these kind of developer partnerships are very complicated and full of unknowns.

The bottom line is that someone will get a bad deal if you do a partnership where the future efforts are unknowns. Many experts would recommend that you keep full control and figure out how to do this deal in a "transaction" relationship instead of equity.

The follow up questions are why OpenCart? Why pick a solution that requires a maintenance team? Why not purchase a pre-coordinated or hosted solution where the maintenance person comes with the hosting. Then hire developers on a transaction basis to make custom changes?