[Agema]

Yes, reinvig, regen and MR are no brainers. You probably want 2 items of MR to be on the safe side, particularly because of assassination spells so don't rely on the battelfield spell for extra boosting.

Important stuff:

You are definitely missing cold resistance (preferably 100%) as mentioned. The other obvious thing you're missing is a load of soak, so a robe of invulnerability or the cut price option of marble armour (bear in mind 50% cold vulnerability and high encumbrance). Your spell buffs most wanted are Body Ethereal and Mistform, which cannot be granted by items. If you know you're facing lots of magic damage, you could skip these as magic damage isn't affected by ethereal and mistform will disappear after the first hit.

You could pick from luck, shock resistance, fire resistance, resist magic. Maybe some missile warding. You could use items or spells for any of the above. I can't stress enough how important full resistance to fire/shock can be against appropriate opponents. Enough lightning bolts will kill even with 50% resistance, and I've embarrassingly lost an SC to heat fatigue because it only had 50% resistance.

Optional stuff:

Fear will combine well with your Seraph's awe via item (eg. horror helmet). Also maybe some aura damage via spell or item (eg. Charcoal Shield, Fire Shield, or there's a low level astral spell.) Not the Vine shield: better to damage than entangle attackers if paralysed, and Awe means you shouldn't be hit much by basic units anyway. The spell Phoenix Pyre could be handy just in case something can kill you.

In terms of weaponry, AoE is standard and usually best. But there are plenty of optional others in some situations, for instance The Sickle Whose Crop... for generating death gems.

That should cover most bases.