An army consisting entirely of slann...
That is so broken its funny - a sinlge deployment drop means you can always decide to go first there fore giving you an opportunity to counter any alpha strike units the opponents have so turn one means you need to summon enough protection to keep the slann alive - this is assuming that you are not going to be able to destroy the entire opposing force with a single hero phase
2x slann and 1x kroak - gives you a total of 10 spells to play with
with an agreed formation bonus of +1 to cast, I think I would probably do the following:
Slann 1 - spell1 - Saurus Astrolith bearer - summon on a 4+ - immediately plant his battle standard
Slann 2 - spell1 - Saurus Astrolith bearer - summon on a 3+ - immediately plant his battle standard
Slann 1 - spell2 - Eternity Warden - summon on a 2+ - deploy within 2" of at least 2 Slann
Slann 2 - spell2 - Eternity Warden - summon on a 2+ - deploy within 2" of at least 2 slann - these two give you an extra 14 wounds of survivability to your slann
Slann 1 - spell3 - Saurus Warriors - summon 10 on a 3+, 20 on a 8+ - deploy in protective ring around Slann and saurus heroes
Slann 2 - spell3 - Saurus Warriors - summon 10 on a 3+, 20 on a 8+ - complete protective ring arouns slann and saurus heroes
Kroak - spell1 - bastiladon - summon on a 5+
Kroak - spell2 - salamanders - summon on a 3+
Kroak - spell3 - Stegadon/Engine of the Gods - summon on a 7+
Kroak - spell4 - Saurus oldblood on carnosaur - summon on a 7+
I cant see anywhere in the rules saying that you have to complete a single wizard's spells before trying to cast with another wizard - please let me know if i've missed it!