From what I've seen, the custom career is simply a way to register your sim with a career when they would otherwise be considered unemployed. For example, if you have a sim that stays home to earn the money through painting, gardening, writing, etc. and don't have them in a set job, you can register a custom career for them (naming it yourself). This only effects social interactions, I believe. So if a sim asks your sim about their career, they would give the custom career you've set rather than being unemployed. There's no wages involved in this at all. I'll likely use this for my stay at homes, even a Professional Parent (as everyone knows it's more than a full time job!).
I'm currently prepping a new sim (through birth to teen at the moment) for the Acting career. It looks pretty fun and I like how the fame system seems to be shaping up. A new town is always welcome although I think they could have done with a few more lots in the residential areas. And lastly, from what I've read, Get Famous comes with a big load of furnishings, clothing, hair, etc. The period clothing has excited me to consider making a game which takes place in the past. I'll have to see more in the clothing to see if that's possible. It would be a nice challenge to play a game without modern electronics.
