[Arena Made Easy]

All estimates will depend heavily on your hero and research.
Level 1 Arena - 900 archers and some melee backup
Level 2 Arena - 1000-1500 archers and melee backup
Level 3 Arena - 1500-3000 archers and melee backup
Level 4 Arena - (Its been too long)
Level 5 Arena - 9000 archers and at least 5000 of melee backup
Level 6 Arena - ~15k archers and some back up, You'll start to encounter a lot more cavs and swords from here and up
Level 7 Arena
Level 8 Arena
Level 9 Arena
Level 10 Arena - Plow through this with max merc order trebs
Level 11 Arena - Semi decent leveled hero and merc order max trebs
Level 12 Arena - Level 60+ high hero, with 200+ brav and merc order trebs.