Paladin + 4 priests

[Apatheist]

BC and Wrath both had completely different mob and player scaling, health and mana pools, talents, heirlooms, etc. The damage portion of holy nova's spellpower coefficient was 16% in BC and 21.43% in Wrath compared to 7.14% in vanilla.

At level 25 you can cast around 4-5 nova's for 30-ish damage (30*5*4=600.) The mobs in Stormwind Stockade have around 1,750HP at level 25. It will only get worse as you level, mobs get tougher while holy nova doesn't scale well.

If you're really into the idea by all means give it a try but it's generally better to do the math first so you don't waste weeks leveling. I leveled priests with full heirlooms and glyph of nova in Wrath too. It's completely different in vanilla.