I have those three completely done (<23 upgrades for each, as well as associated effects), and I feel good about the gameplay between them. I'll add what I have for the others below.
Game modes aren't too difficult to create, but were you thinking different objectives? (Phantom, capture the flag, etc?) That's a nice idea.
I think ELO can be added later. Gameplay is more important in the beginning.
My item system isn't done yet, but I'm only allowing a hero to carry one item, and have that item be a consumable. From what I read in this thread, you guys were thinking about equipment, which I don't think would work well in this game.
Spell upgrades work a little differently in my version. Each hero has 7 spells, one basic, six advanced. The advanced spells are divided into two trees. A spell must be bought, upgraded, and upgraded again to get to the final form. This is to get players to choose what they want to concentrate on. The costs increase for spells higher up in the skill tree.
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The Baneling morph is more like the light mage l1 than anything else. 2s of invincibility and slow movement with a splash explosion at the end. It's more a spell than a morph like ultra.
The speed spell is mostly about stacking with other spells. It's upgrade adds afterimages (temp name?) that spawn periodically and can get an attack off the target before they disappear. You can run circles around your target and do a little bit of damage, as well as a slight bit on anyone chasing you. It also deals with stim zealot charge (and chain charge with the afterimages) quite nicely. Charge normally guarantees a hit, but w/ this spell the ling can move across the map with zealot chasing behind.
The way I think ling should be played is hit and run, and I chose these spells to reflect that.
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Well here's my progress otherwise:
partially completed archer, lm, summy, dm (turns people into sheep
) and mech, but I need more spell ideas. I've also started on
a stalker hero that focuses on movement/positioning,
a reaper (assault replacement) with stuns, n
and a very fun ghost, almost done (snipe ability that does more damage the longer you target w/ matching targetting sights visible to target as well, slow emp missile, nuke, seeker missile w/ stun, and night vision as well as listening to enemy chat, needs one more spell idea).
I don't have ideas for volt/sin yet.
None.