No Exp or leveling, ever.

Disabling experience gained is easy, there are many ways to do it, one being setting those 6 bytes to $EA:

Code:

C2/5E4C: 20 35 62     JSR $6235      (Add experience for battle)

C2/5E56: 20 35 62     JSR $6235      (Add experience for battle)

For your starting level, the actors starting data only allow party average -2 to +2 iirc, There is once again more than one way to set a custom HP / MP one could perform a custom party average on the character (event command $77, see C0/9F32). But personally I would modify the event command $40 use at character recruit (see C0/A07C) and get the correct HP / MP /level(?)) from 2-3 tables, one for each data. You could use actor ID as table index. This solution (or any in fact) require a fair understanding of assembly coding, so it's not something you can achieve without actually putting both hands in assembly learning.