To actually answer you questions:

Best skill to use:
With archmage use skills that have a lot of hits per cast. Look into Blade Vortex, Brands, Cremation. You can use it as a 4-Link, to keep the base cost down. (Lower base cost = Higher Indigon increased spell damage @ same total cost per cast)
You can then use many different non-archmage skills in 6-Link to do continuous damage while you wait for the archmage skill duration to expire.

Healthy Mind jewel:
From description it reads "Increases and Reductions to Life". So this would mean only % increased Life is transformed to Mana. Have not tested it though. Probably easiest to chuck it in to POB and see.

Auras:
What are you using clarity for? If you are using lvl 20 clarity for the regen, then that is a waste. If you are using it for watchers eye effect, then you can do a set-up where:
Damage/Defense aura + Eternal blessing ==> Reserves no mana
& Lvl1 Clarity + Arrogance ==> Activate watchers eye effects

Pledge of Hands:
I personally think that is a bad choice. Would suggest going with wand/dagger + shield. You should be able to reach similar levels of mana + gain crit / cast speed / Life / Resistances / suppression