Some questions summoner build.

So, i'm doing a summoner build based around damaging with Minion Instability. This is the build:

[www.pathofexile.com]

As you can see, i'm using Elemental Equilibrium and Avatar of Fire. Do they stack? Will an enemie still get the debuff from EE if i use like shock nova? Or will the shock nova just miss?

My build is based around getting my summons as high hp as possible. What passives work on Minion instability? spell damage? elemental damage? fire damage? is it considered an area spell, so can i increase the area size/damage?

Minion Instability's damage cannot be increased. It will always deal 33% of the minion's maximum life.

Yes, EE and AoF would "stack". The elemental damage you deal due to EE would be converted to a different element with AoF.