[Snake]

Void should have its own damage type yes.

I'm not sure if it should actually cause 50% damage back to its user, thats quite alot of damage.

It's intended to be big, as for the user is wielding the void without protection. That's why if you're fighting/using void, you'd need to be clad in Nullstone equipment that I've also suggested.
It will not only reduce the recoil/damage (notice how I said 'reduce Void damage taken', works for the prepared enemy AND the prepared Void caster.), but also heavily cripple the chances to get 'injured' with void poisoning, because the damage will hopefully be small after a 75% Nullstone equipment damage reduction.

Andddd...

using the void is akin to slowly getting cancer from working with dangerous materials, Its a thing to RP as time passes on, (my character uses the void enough that I rp having a coughing fit after long strenous fights.)

It'd be better to make using a void skill/spell take a % of the users current hp
1% for voidgates
10% for blackbolt/detogate

I thought about it too, makes sense to lose a fixed amount of HP, though, and that's more a Ghost thing to 'use HP to damage'. Having Void to simply do recoil damage would make it a bit more unique, and that's my main goal. Give Void damage a 'trademark' effect.