get Intuos if you are really got the long term continous drawing thought!!(can be use for few year!?)
get Graphire if you arehappy to try...save up money
(also there might be some second-hand to try?troublesome this way?)
i got a A5 working size intro3 (the second smallest one?the average one)and i feel very fine because i used a lot of A5-paper to draw ............even now!!!no scanning in years^^
i think 4x6 with work perfectly OK...
but you just got to get use to it(some people happy to be a PRO of pencil!!can you!?)
i have not yet see people talking a lot about the sizes of they tablet?!?!?(they loved what they pick?)
get some digi-art-magazine....
quite very very very often they talk deeps into "tablets".at least a hell better than my "advise"?