I have a big FastPass FAQ on my web site with details about the system if you are interested. But to briefly answer your questions:
- you can hold more than one FastPass at a time. Typically, you can get another every 45 to 60 minutes, although it may be as long as two hours during busy periods.
- you certainly can! There are no pre-determined limits on how many FastPasses you can get per day, both total and per attraction. So if you wanted to, you could keep getting passes for the same attraction throughout the day.