Actually, 4 LODs are quite minimum for addons. I would recommend 6 or 8 at least.
The CFS3 gmax tools will only work with CFS3. Unless CFS3 uses the same file format and so on as OFP does. Which is highly unlikely since BIS have made or modified pretty much everything for their own use.
Completely new 3D models get into OFP by a program called Oxygen (or O2). That is the tool used to create all the models for the game.
It will be released some time in the near future (no date has been decided) and you will be able to use that to import models to OFP.
There are only some limitations:
O2 can only import .3DS files.
So unless you can get your .gmax files into .3DS you can't use gmax for OFP modelling.
Sorry.