I understand you want Chaos caster that has smooth leveling phase / progression curve.
Actually I think Chaos FoI could work but let’s skip it because it may be tricky sometimes.
(the best Chaos FoI I know uses 2 Arcane Sparks for Energy regen)
I think it’s the best idea. Farm this off-hand as well Abaddoth’s Sermons
(can also be farmed in the 1st act just as the scepter you mentioned) for full Vit conversion.
Maybe also try Vid-Touched Ammo as a filler for the lols?
Of course this is beginning leveling, later maybe switch to some proper Chaos Occultist
(that can still use Chaos Sigil, there are a few builds like that), i.e. Black Scorch Covenant
If you play Deceiver, I highly advise you to mod Inquisitor Seal to be Red instead of defeault Blue, assuming you don’t items with skill modifiers that change it on their own.
PS Also this shield is very good Vampiric Bonewall