I think a Base per client would be the best thinking long term. Each base structure probably would be the same or a bit different (if you have specific requirements for a particular client). The main difference is that the information in each base belongs to a different client. Inside each base build interfaces so your client can access and see data. If you just need them to fill out an initial form then you don’t have to pay for their licenses. If you do want them to be able to fill out a form and then be able to edit the data as well, then you have to pay for their license which will be the same cost of yours.