Charismatic yes! I totally agree with ambitious (but isn't that true for all careers and I don't think it should be an requirement). I would select athletic instead, well not muscular but cardio, since models have to stay thin. Some of the special work opportunities could be working out for x number of hours to increase work performance.
Another interesting thing would to make the level of celebrity important - if you are to rise to the top and become a supermodel you should probably be quite famous as well. Or it should at least give you perks.
However, consider which traits came with witch expansion - if you want as many as possible to be able to use your mod I would suggest going only with basegame traits as opposed to the diva trait or even the celebrity points.
And yes, you totally need a portfolio! Maybe one of the settings for work performance should be photo shoot?
My suggestions for the different level names (totally based on watching Top Model) and keeping in mind that being a model is about advertising new products...
1 - Walking Billboard (or a better named equivalent of handing out flyers for something)
2 - Mall Model
3 - Catalogue Queen
4 - The Face of....(insert famous Simmish product)
5 - New Face in Fashion
6 - It Girl
7 - Designers Pick
8 - Front Cover Model
9 - Runway Diva
10 - Supermodel
You could also go the seamstress route - but to me that seems as if that career choice should end up as a Couture Designer not a Supermodel.
Wow, seems I'm more invested in this that I originally thought