1. You added euplatesc.ro as gateway for Romania but not that many website owners use it as they have terrible conditions for new merchants and they don't accept new users very easily and they have big taxes. For example I purchased it and euplatesc.ro did not even accept me because my company is too small for them.
Main payment merchant in Romania is NETOPIA Payments (
https://netopia-payments.com/), they have higher acceptance rate and lower taxes. I would suggest you implement this as a new gateway for Romanian users. They also offer installments payments, Google Pay and Apple Pay and also have the possibility to save cards for users, via token. All payments are made in a new window on merchant's website. No data for cards is saved on the server so this also can be implemented quite easily.
A great thing that NETOPIA offers is recurring payments, this can also be implemented in Osclass Pay to be able to purchase monthly/yearly packs or user groups or maybe like a yearly Prime membership.
2. a. If we activate Product selling, let's say user X sells products valued at $10.000 on our website. How can we see how much we need to pay him and mark that payment as processed? I'm not sure on how this really works.
b. What if we went to charge like a 5% for providing the service to sell on our website? It would be a nice implementation.
Looking forward to your answers. Thanks!