get a case bigger than you need. extra room will be welcome if this is your first build, more room to work.
unless the monitor is built into the case there is not reason it has to be pretty. you spend all your time staring at the monitor not the case.
do not get a case with a power supply unless it is a proprietary form factor, then I'd suggest staying away. first build and all. stick with standards ATX/ITX/EATX etc makes replacement parts easier to find
to really answer your question I'd need to know much more about your needs from the PC, will you need 3 DVD drive bays, which motherboard form factor, etc.
without knowing more all I can do is give buying advise.
use this list when deciding on a power supply. spending more on a power...