Ok do you want to be a blood elf? if so you will need the burning crusade expansion, You can do without WOTLK til 68.
As for classes it really depends what you want to do, If you want to be a melee combat class a warrior or rogue is a good choice, If you want to be ranged then a mage, shammy or hunter are good choices, If you want to be a healer then a priest or druid would probably be the best choice.
Druids(fun) and paladins(boring to play trust me) are hybrids and can do everything the game has to offer but the druid is the most customizable and fun class imo.