First off, bare in mind this software is very generic, so it can be adopted by lots of companies from different industries/sectors so it’s common to not find everything included out-of-the-box.
I am assuming here that you want to create a marketplace like Amazon. If that is the case, we’ve implemented marketplace projects already so this is absolutely possible to be done with ScipioERP. However, it may require a bit of customization depending on the path you take eventually. I also assume that you took a look at our documentation, which may not include all you are looking for, but can serve as a good starting point:
So, answering your questions briefly:
1,2,3: You can implement this in different ways and probably the most easy ones would be: having multiple stores with a single catalog and bind vendors to each one or having a single store with multiple catalogs, so each catalog belongs to a vendor. Both may have their pros & cons but this is something one can be done without code changes (or just a few). Basically, just data adjustments. I’d need more input about your specific scenario to give you a more appropriate answer.
4: Can you elaborate further? Which parts don’t you understand concretely?