General Witch Help Requested

So, I've been around the beta for awhile now, but had to take a fairly long absence due to life. I'm coming back however and SO much has changed and been modified. I believed the last class I had off hand was a 61 Shock nova/spark witch in .9.5ish?

So, I'm looking for ideas and thought firestorm would be an interesting change of pace and spec. The spell design looks amazing. What I am stumped on is what to do in regards to the passive tree and other spells to really mix with it.

Fireball, at least reading the feedback threads, seems to be on the disappointing end of the spectrum right now. But it would synergize well with the build.

I thought about Ice spear for single target goodness, but my passive build will probably lead to fire passives and not cold. so I wonder if it'll still be worth the use.

Spark is in the same vein, no passives aimed at it, so will it really be a solid single target ability.

For a few backup spells, temporal chains and elemental weakness are obvious choices. I'll probably find a way to work in 2 curses, but not a given. Something I need to find out if it is worth the points.

For Armor, is it worth it to build as a straight ES or more viable now with 9.7 to aim for a hybrid Armor/ES? I wasn't a huge fan of chaos innoculation before, so I'm curious how it holds up now in the new difficulty settings.

Now, the passive tree itself, I have a few questions. Obviously I'll be aiming for the fire damage nodes. I'll need a decent amount of INT, some dex I'm sure as well.

Are the Area Radius passives good for a firestorm focused build? Or does it make the fireballs more erratic than they already are?

Are Mana regen nodes worth it later game or in general? For the most part I always skipped them and had little reason to need to worry about them, has this changed?

That's all that is coming to mind right now. Thanks for any and all feedback and help!