==Rough Calculations==
I am basing the minimum amount on Extra low cost training ( RT11 ) because it gives the best Hero XP per recruit, best Hero XP per 1k food, and requires zero ascension items.
If a player needs 4* Heroes, then running three camps at Extra low cost training ( RT11 ) and one camp at Legendary training ( RT20 ) for an average of one 4* Hero per 10 days and an average of one 5* Hero per 40 days. Using duplicate 3* heroes for 4*/ 5* 3.60+ leveling.
Or just running four camps at Extra low cost training ( RT11 ).
Add some variation for Rugged clothes, free token/ free gem summons. Add some more variation, but not a lot, for players who like Uncommon ( RT02 ) and Common ( RT01 ) training.
If you are using your training camp heroes as they finish, your Level 20 Watchtower and Level 20 farms should be able to keep you in food.
So 2x- 3x rainbow 5* 4.80 ( 10-15 total heroes ). Closer to 3.2x rainbow 5* 4.80 if running four camps at Extra low cost ( RT11 ) with occasional Extra fast ( RT19 ) and players who decide to use Uncommon ( RT02 ) and Common ( RT01 ).
==Only leveling 5* Heroes==
But as I say above, if you level all 5* Heroes, you will not have any training camp heroes to level heroes to 4* 3.60/ 4* 4.80.
That is why I suggest, even if you are a cash player, you get four rainbow 4* 3.60 teams and two rainbow 4* 4.70 teams before trying out your first rainbow 5* 2.60 ( with no 4* heroes ).
==My partial rainbow 5* 2.60 team==
Right now my rainbow 5* 2.60 team is waiting for 1- 2x 5* healers, 1- 2x 5* splash damage and a 5* green. I have two red 5* 2.60, one blue 5* 2.60, one purple 5* 2.60, one yellow 5* 2.60 but they are all solo heroes, no synergy, no healers and either attack all or snipers.