you can go either way.
For managing accounts and privileges, check out ...well...File > Manage > Accounts & Privileges
There are many options for limiting view, edit, create, delete, by table, by script, by account...simply make a custom privilege set.
The choice of whether to build 1Dbase with 3 tables, or 3Dbases is typically not made based on the software, but on how you will use or maintain it. The software doesn't care all that much, either way is fine.
if you are new at the whole thing, consider making it all in one dbase...your demands on it most likely don't warrant splitting it up (but that's a wild guess and should be taken as such).