Funddevi: This depends on the relative prices, how much you are willing to spend/how long you are willing to spend saving, and how portable you want the tablet to be. I’m thinking that my next tablet will be a smaller one (compared to my current, which is bigger than my laptop!) so it can fit in my laptop bag, so I can use it other places. Other than that, my instinct would to be to go with the larger size, for more precision (feel free to correct me if I’m wrong, blenderheads).
Atemporalskill: This is the calibration of your tablet. This depends on what OS you’re using, the driver, and also the brand/model of the tablet. A good bet is googling the “[tablet make], [tablet model], [drivers]” if you’re in windows. For linux google “[distro] [tablet make, model]”. For Ubuntu this often involves editing xorg.conf.
Always remember that (especially here) more input means more output!