Big as you can afford! I can see some of the loop apps chewing up memory if you aren't careful, and what's your current fakebook library size? Mine's a few GB. There are a couple of rumors about an SD slot, if true, that might solve THAT issue once and for all!

I don't know about the 3G plan, maybe iPad2 will be Verizon capable, and it might be a bit cheaper? I think April is touted as the most likely launch of the iPad2. As with most things from Apple, the second version is usually WAY better!