as i have played this game for a few years ill try to anser your questions.

firstly theres a lot of patches around the 400 mb mark- so all up your looking at one huge download to start playing my advice is that if any of your friends play the game copy there game folder (the entire thing over) as that gets around the downloading of patches, or you can copy the patches over and load them on but copying the whole thing is super lazy which i like. If you cannot do that then i guess you will have to wait for the downloads. I played alliance for a long time, but swapped to horde as i found that faction preferable as there are less morons, but more abusive wankers.

Potentially you can play it with dailup speeds, though you will be severely limited endgame. However when my 12mb connection gets capped, it still goes back to dialup speed, at which point i can still play most content except for large raids and going into big cities at peak hours.

Paladins are no longer limited to just healing so that is an option, other then that warriors are pretty strong but also have their limitations, i cant suggest a class because only you know what you will be able to enjoy, however i can strongly suggest against shamans as they are pretty much shafted at the moment. The class deathknight, has pretty much the same principles as a warrior, plate armour, big weapons, has limited spells (do spell dmg attacks) and is able to enchant its weapons, however you must level a character to 55 then make 1 which also starts at 55 with a free mount and free gear so thats always an option. A deathknight can be anyrace, personally im not a fan of deathknights though so i cant suggest which race is the most beneficially, however humans get some decent racials and dwarves are pretty good at axes and if you want to be an evil death dealing midget, gnomes are the way to go.