Ideas and suggestions.

Regarding the first point – in this version, Water becomes stronger than Logistics in the late game; just one movement restoration spell alone justifies taking the school, and the other spells are also enhanced. Plus, the blue hat is enhanced with an additional control spell.

Regarding the second point – it's a very foreign mechanic for Heroes... limiting teleportation based on the number of hit points... it's better to introduce some other limitations.

In Heroes 5, there's a certain number of creatures per mana unit. However, this isn't the best option; instead, introducing a coefficient that depends on the level would be good.
For example:
10 creatures, level 1, for 1 mana
7 creatures, level 2, for 1 mana
4 creatures, level 3, for 1 mana
2.5 creatures, level 4, for 1 mana
1.5 creatures, level 5, for 1 mana
1 creature, level 6, for 1 mana
0.5 creatures, level 7, for 1 mana
Or, depending on the growth rate, but that might be less elegant.