Using FTP (I assume you mean SFTP) will buy you some performance, as would other protocols that are faster and requiring less compute than SMB.
I predict whatever solution you use will only buy you time. Usage is bound to increase so you’ll still hit the performance limits for the hardware platform at some point, unless you can constrain the simultaneous connections. File sizes will impact scalability a lot as well.
You can’t guess this one. You need to test.
tl;dr - I suspect you can’t win.
Bastard.