I'll give you an agree because I've seen some amazing mods out there, but as for me, personally, the only thing I've managed to do is make recolors with S4Studio. But I have to say it was a pretty simple process and felt very gratifying. It was my first foray into any kind of "custom content" in any of the sims games.
I'd like to do other stuff but I just don't have the ambition or know-how to do anything substantial. Did they ever make it easy to make custom careers yet? I remember there was a way early in TS4's life but after all the expansions and patches it apparently doesn't work anymore.
smash that disagree button fam, red's my favorite color