Don't know about the second question, but... I would go with a G-tech for a hard drive. I love mine, really durable, USB, Firewire 800 X2 ports. I enjoy that it was time machine configured too right off the bat. I have the 320 GB but get whatever fits your needs. We have a pc back home and we use westen digital for that, it works fine as well, I just prefer the g-drive.
The best way to backup your external onto your main drive is probably an .iso disk image. Probably a little more compressed than a .zip and just as easy to make (with the right software that is obtained rather easily). As far as drives, I have a Seagate 1TB drive and its worked very well for me, but so would WD.
And as a side note I would also agree with the enclosure idea. Very easy to do (they usually come with clear directions) and often its a matter of putting in a few screws, nothing too difficult.