1. With a desktop, you get more PC for the money and you can have a nice 22" or 24" screen. That makes operations really pleasant. But, of course, you have no mobility. If you want mobility for basic function in addition (mail, internet, etc.), get a Nexus 7 from Google for $199. That thing works very well for that purpose.
2. Regarding Windows 8 it is difficult to advise. Some people like it, some hate it. I have used the pre-releases since day 1. It is a nice toy but I would not put it on my main systems. I will get one copy of it that I will install on an eSata or USB3 attached disk - just to stay up-to-date.