Medic is gonna be a tough one, why? He already has a bunch of good upgrades, so some of these will just be tweaks to those and add extra upgrade levels to them

Medic Upgrades

A series first! we'll be looking at the Medic tab where the resistances are and just adding a +3 health for regen which has 3 upgrade levels, each costing 100 credits.

Mediguns

An upgrade that when bought will ask you which medigun's uber effect you want for your medigun, this means you can use the quick fix's quick healing and mobility while also having the Kritzkrieg crit uber effect. Since this would probably be broken, make it 450 credits, you can reset the uber effect back by refunding the upgrades.

Medigun range upgrade, increases your medigun's range by 1 Pyro for each upgrade level, that's gonna be my unit of measurement for the upgrade series. Has 3 upgrade levels and each costs 150 credits.

Medigun upgrade that let's you attach the beam to robots to slow them down and drain their health which helps build uber. Costs 300 credits.

An extra upgrade level to the Projectile Shield upgrade. This upgrade costs as much as the other upgrades, and will not only block projectiles and hurt robots, but will now reflect projectiles that hit it and push robots that come in contact with it, kinda like the end of the Sound of Medicine short film that Valve made.

Primary weapons

Extra health on hit for Crusader's Crossbow, increase health on hit by 50, has 3 upgrade levels, each costing 100 credits.

Mad Milk Syringe upgrade will now heal your friends on hit, how ever each syringes only heals 25 health, so either constantly shoot them, or just use your medigun.

Melee weapons

Upgrade for the amputator where when it hits your friends, you heal them up to full health, this has a 25 second cooldown and has a bar at the bottom right to show you when it's ready. If you don't understand still, think of the shock therapy from TF2 classic. This upgrade will cost 150 credits.

Upgrade for the Vita Saw increasing how much uber you keep after dying, costs 200 credits.

Upgrade for the VIta Saw where you get the old Vita Saw's trait of 25% upon spawning, costs 175 credits.