Given the time it takes to level, and that it's not practical to level in groups higher than 5, and also since it's your first time playing, I would start with just 5 (never thought I'd say JUST 5 lol) and learn from there. Once you have 5, you can then get 5 more accts, and repeat, and keep doing so until you have your 25. Or you could just use the same accts and transfer off later depending on how fast you level. Then you don't have to worry about monthly costs for so many accounts all at once. I honestly think it will be boring with all the same type of character. I'd make one "holy trinity" group, with a paladin priest and 3x mages for your first group, then make 5x shaman, 5x locks, 5x druids 5x mages. Or 5x of whatever dps you want, with at least one of em a hybrid team so you can off heal/offtank. Or I guess you could make em almost all shaman, with a team of utility toons (mage for water and portals, lock for summons and ss, druid for buff/offtank priest for mana/health return.