The best advice I can say is CS-Cart is what I would consider an MVP of a marketplace. It gives you a head start in launching a marketplace vs. building one from scratch....but you still need to do ALOT of your own custom development to "make it your own".
We have invested about $30,000 in the past year customizing the solution to meet the needs of our vendors. It's gotten us to an "ok" place, but we still have a lot more work to do.
Also, a bunch of our development was HIDING things we didn't want vendors to see. CS-Cart shows everything by default to the Vendor even if the functionality is useless to them. This makes the vendor admin panel more confusing. We feel "less is more" and you should only show the vendors what they need to use. When you start showing them things like user groups it just makes them scared and they run away.