How to price SaaS, Need advice

I am building an online marketplace for service providers. The service provider will have the option of two profiles, basic vs. premium profile. My current thoughts on pricing structure are as follows.

Basic Profile - Limited feature set - Free + transaction fee

Premium Profile - Full feature set - $25 a month + smaller transaction fee

How large should transaction fees be in order to not have vendors move off platform / be discouraged from working with us but still enough to make some money? What’s the sweet spot?

Should the transaction fee be taken from the vendor side or on the customer side as an additional charge at checkout?

Should there be a small flat fee put on transactions?

Any other things / options to do?

Any advice on this would be greatly appreciated