Just to be honest, I'm mostly interested in your mod for the ideas that it gives me for my own. Without getting into specifics, you've got some solid ideas.
Since you seem to be able to do things I don't know how to do yet (i.e. make Vikings missiles not home), maybe you can figure this one out for the Medic. Your rendition of Terran Bio is based on harass, which I like. They're fragile and less all powerful than in HotS. I feel like bio should crumple to high tech units and splash damage, but be pretty effective vs other Infantry. To this end, I suggest an addition to your Combat Shield upgrade for the Medic. Give the unit +20 HP and also allow use of the Combat Shield ability. This ability is ground targeted. The Medic plants her shield in the ground, losing the +20 HP bonus (and losing the shield from her model if you know anything about modeling

Imagine using your drop pod with, oh, say 4 marines, 2 marauders and 2 medics. You land down near some minerals in an enemy base to kill some workers. Clump up your bio in between some minerals and have your medics drop their shields to seal off one side of it and buy the bio some time in case of a counter attack.
If a player is going more of a pure bio style, these shields can level the playing field a bit to make up for the loss of Conc. Shells vs melee units. A moving zerglings will have to go around the shields, and same with Zealots. If you've got a decent bio force and put down a nice big wall of shields vs a melee heavy force, that might make the opponent pull back, or take the time to kill the shields will ranged units before advancing. This could buy you time to retreat and be used defensively. Doesn't have the brainless massive power of Conc shells where nothing can escape.
Ideally, there'd be some way for a Medic to pick up a single shield again (and regain the +20 HP it offers). Maybe have a short cooldown on the ability to prevent weird abuse cases of medics sticking a shield down, and picking it back up again quickly. To prevent spam and "immortal" shields in low # unit situations (i.e. 2-3 zerglings can't kill the shield before it's picked up again, and the medic spams it). Meh, probably not a big deal.
Have placement be like the auto-turret: it has to have a valid clear location and a footprint.
Imo, that would give the medic some decision making and micro, and a risk/reward scenario. The decision is will my army last longer if I keep the sheilds on the medics (i.e. they're being targeted, usually by ranged units), or will my army last longer if I can set up a brief fortification to buy me some time from melee units.
Potential problems: if the shield is too small in size, it doesn't make much of an impact given how tight clumping and pathing is in the game. It's only applicable in small chokes or vs mostly melee armies. I've thought about it giving nearby units +1 armor to give it a role vs ranged units (hiding behind the shield), but many people dislike the idea of auras in Starcraft and I don't know if that would case significant lag if somebody decided to build 20 medics and shieldwall the hell out of someplace and stick 25 marines behind them. (I know you can set stacks so only one instance of the aura can apply to each unit, like Guardian shield. Oh. Guardian shield's an aura, so that's not too big a deal. The radius would be way smaller, just like within melee range of the shield.)
Anyways, that's my idea for Medics. Thoughts? Keep on making your mod!