Op here. Thanks everyone for the replies. To clarify, I do back all of my music and other files up onto an external drive, I'd just rather not be chained to that drive to listen to my music. I'm also curious as to how easy Apple will make it to download just a few songs at a time from iTunes in the cloud. For example, could I download a whole playlist that I'd made before I matched, or would I have to manually remember and select each of the songs in the playlist for individual download?
1.) If you do not want to lug around your hard drive. The two cheapest alternatives would be to wireless remote access one of your home computer's iTunes and play your media over air through your other home computer. OR (do what I did for my MBA) Attach an external hard drive to your wireless router and access your media anywhere you have a wifi connection. Most places have wireless nearby to either stream the information directly to your MBA or momentarily use the free wifi to download your media to your HDD on the MBA.
2.) If my memory serves me right the iCloud feature will download your purchased content through iTunes to your other "i" devices. I do not believe that you can directly stream from the cloud but pull information from it to store on your physical HDD. So yes, you can download your whole playlist iTunes or not assuming you have iTunes match.