get a refurb from the apple store or check out
www.dealmac.com for newer old stock apples. many good deals there!
if using the ua-5, you will probably be using a usb cable, and some people have success with 24/96...others don't. usb has not been proven reliable for 24/96.
aif (audio information file) is the standard audio file for macintosh, and it has a 2gb limit, as does wav. this 2gb limit is a problem if trying to record 24/96 as an hour show/set will probably bring you over 2gb. i believe only the discontinued tcelectronics/works spark xl 2.8 (and above) has a file format that will allow recorded files over 2gb...i think its wav64 or SDII.
you can do all the editing, tracking, and flac/shn conversion on the mac, and all the audio editing programs that i have used have an option to save in aif or wav. get xAct and you can convert aif to shn or flac without having to save to wav.
anyything else to know about owning a mac...yeah...once you go mac you never go back! you will be pleased!