The Professional and Ultimate Edition licences both contain the .psd files (the others do not). The Ultimate Edition licence is MU enabled, the Professional Edition is not. You can see the side-by-side feature comparison list here:
http://appthemes.com/themes/jobroller/#features
The 50% discount only applies to those who are signing up to our preferred hosting partners via the AppThemes homepage, so if you already have an account you will not be eligible. You can read more about the requirements here:
http://appthemes.com/promos/
Yes, you can certainly choose to have free listings, and only charge for featured ads. At a later date you can update the ad price if you wish. Note that if a customer places an ad, and you then decide to charge for ads/features ads later on, that the customer can't edit their existing ad to make it featured after the fact...they would need to create a new ad.
No, there is no setting for a maximum number of featured ads.