Tried a few brutes out...

And I have to say, SS/FA is AMAZING. I can already at lvl 23 do -1 x 4 for my missions! half the time i can afk in the spawn with my aura and my toggles on while spamming the heal and come back to a dead spawn.

But I notice i need way more knockback/down/up protection and some ranged / mez resist.

What powers should I take to alleviate that (and IO's to fill the void)?

Thanks in advance

temperature protection,

two slots -

steadfast protection kb proc
steadfast protection res/defense.

Fiery Aura is a little different from the other armor sets. It doesn't have a dedicated toggle for it's mez protection. You get hold and sleep protection from Plasma Shield and immobilize from Burn. It also has no knockback protection a t all. You will have to resort to IO's for that or Acrobatics from the leaping pool. You can also get immobilize protection from combat jumping in the same pool if you don't want to use burn to provide that.

As MrHassenpheffer said the Steadfast -Kb will give you 4 pts of KB Protection.
You can slot another of those in another Resist power or the Karma -Kb in a Defense power for another 4 pts.

Blessing of the Zephyr also has a -Kb IO but is a lot more expensive than the Steadfast/Karma (so Ive found but with the crazy markets currently your luck may vary).

Some sets also provide Kb protection like Kinetic Crash (KB IO Set) with 4 slots.

I prefer to have at least 8 pts of Kb prot as this will cover you for the majority of your toons career (not ALL scenarios but a HUGE chunk of them).
As always you can opt for more but it depends on if you will gimp your toon in other areas.

I'd say that either 1 -kb IO or 3 is what you want; 1 IO will protect you from most things, and there's little or nothing that 2 IOs will stop that 1 won't. There isn't much that is over 4 points kb but under 9; so the 8 points from 2 IOs isn't much use.

So do the knockback protections work against knockdown and knockup?