Welcome back!
The best answer I can think of is don't add anything until you've had a good think about what you want in your game. I have many dozens of aftermarket mods, but each one does a specific thing that I want to see. Not one of them is absolutely necessary. If you have any questions on what specific mods do, please ask.
One thing you should have that is not a mod at all: SH3 Commander. It does for your career what the supermods do for your game.