Paladin + 4 priests

[Apatheist]

Renew doesn't stack.

Holy nova costs from 185 mana at rank 1 to 750 mana at rank 6 and does negligible damage (7.14% coefficient.)

In your 20's-30's you'll be OOM in 3 GCD's and you definitely won't clear dungeons spamming holy nova.

There's actually a video of a guy farming with holy nova here. His talent build is entirely based on reducing holy nova cost and he's stacked intellect on all of his gear. He can cast holy nova 10 times before he's OOM -- hitting for around 200 damage per cast. That's 2000 damage plus crits before you're dry. To put that in context, the ogres in Dire Maul have around 14,000HP.

[Fuzzyboy]

Renew doesn't stack.

Holy nova costs from 185 mana at rank 1 to 750 mana at rank 6 and does negligible damage (7.14% coefficient.)

In your 20's-30's you'll be OOM in 3 GCD's and you definitely won't clear dungeons spamming holy nova.

There's actually a video of a guy farming with holy nova here. His talent build is entirely based on reducing holy nova cost and he's stacked intellect on all of his gear. He can cast holy nova 10 times before he's OOM -- hitting for around 200 damage per cast. That's 2000 damage plus crits before you're dry. To put that in context, the ogres in Dire Maul have around 14,000HP.

I can assure you that I did work. It's not just theorycrafting - I levelled a team of 1 paladin and 4 priests through SM, ZF and BRD, using just Holy Nova spam. Granted, this was during the TBC expansion (or WotLK - I'm not 100% sure), so I don't know if they did some changes to Holy Nova between 1.12 and then, but I did work - and exceedingly well.

I was never in DM with that team, so I can't say anything about that instance, but I was in BRD at similar level (50'ies - and the elite mobs there have around 8k HP, so thats not far off.

[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.