I'm also making a save file rn, hope my answer isn't too late! :#
Anyway, I suggest using cheat codes instead of having Sims call so you won't have too much time passing in-game.
To add a career, open the cheat console and type careers.add_career career name. Obviously you'll replace career name with whatever career you'd like the Sim to have. The actual career names used for cheats don't always match the names in-game though, so you'll have to google them as needed (it's a pretty long list by now, so I don't wanna paste it here).