Well, let me give you a few pointers with the response
1) For heroes and abilities, don't use slowing (make the reduction small perhaps if you want to keep it) or stunning (1 second or nothing). If they're so bloody upset to want to use cheap stuns, since the guy keeps running, just blow up their bloody base and where does the guy have to run to now? EH?! Also, if you can help it, either take off wind walk altogether, raise the cooldown to be inefficient, or take off the critical attack. I have no problem with 00bar speed and invisibility, but I HATE suddenly being killed by a critical and then a spell of a sort like storm bolt--high damage and at a range. Obviously, this should just be done by changing/removing Buffs, effects, and some data scores to 0.
2) Spell making is pretty difficult and, if I recall correctly, sizes up the game quite a bit. Still, it could be nice to make a few different graphic in spells.
3) Yep, classic AoS. Make sure that the stats is the SAME! I've played a few games where people try to make it different by having someone's melee have lower hp but higher armo, lower damage but higher speed, and et cetera. In the end, it becomes one sided when you notice one side losing 75% of the time without the help of a hero. By all means, just change the model and sound of either side's units.
4) Good idea. Better be destroyable by a hero, though. You could also go to either make a Hero's death worth the hero's level in kills, or just have the separate "Hero Kills" that perhaps could spawn something larger than a Super Creep, for offensive and low-defensive players, who have a knack for killing a lot in their area--which ends up being small.
And a side note--MAKE THE AREA LARGE!! A lot of these games have way too many twisting passages. It's not really that I can't navigate through them or something, but it sucks to have to go get special items at the end of said passages and then have your fortress taken down--your hero takes a long time to navigate out of the pit. And teleportation rods are no use, their cooldown is too high, not to mention the valuable casting time.
So, make a wide open area and a huge fortress. Don't go bananas with the doodads though, just make the map as large as possible and make a lot of it empty space but with coolness--larger buildings and doodads placed in such a way that it gives the same eye candy effect that an inefficient placing of many doodads does. I might, if I can get my skins working, make a forest doodad to make a slightly smaller polygonal model for those who like having large forests but either don't like placing all the trees in blocks or feeling the lag when they load a map with thousands of trees.