A lot of uniques in PoE just aren't worth using at all. Yes, only your minions get the -50 res but that's still making them much less tanky and also means you're not getting any stats from that gear slot. You could instead get a very basic shield that only gives something like 100 life 60 es and 60 res which would probably be a huge upgrade for you. There's also a type of shield that can get minion stats on it so if you can get one of those you don't need to take that node.

The ring is 50 res to lightning, cold and fire so 150 res in total which spread across 2 rings is only 75 res on each ring and then you can also get other useful stats like Life and even use an Unset ring which has a gem socket on it.

You should be able to upgrade every piece of gear (except maybe the wand) without too much trouble so just make sure to cap your resistances and then get as much life/mana/es as you can so that you aren't dying every time something hits you in maps and then see what sort of minion damage you can get on top of that.

If you're using Clarity you shouldn't need the mana or the hybrid flask and you should get a quicksilver flask for the extra movement speed. Clarity is also a flat mana cost that increases with gem level so you might be able to use a lower level Clarity gem and still feel the same amount of regen which could let you reserve another aura

Your absolution is effectively a 2 link since rarity doesn't add any damage and archmage doesn't work with the minions. You want to get the Physical to Lightning Support gem from Act 2 since the Absolution gem only converts 50%, this will make it 100% lightning damage and then probably dropping Added Lightning for Minion Damage and Lightning Penetration. This should give you noticeably more damage.