bo spirit -> splendor low str
fcr ring -> soj
maras -> 2/10/50+mana amulet
can use a memory staff for precasting ES and investing less hard skill points into it (up to +9 ES on memory)
also, you don't really need 95% for pvm. aim for 90% with precast, everything dies pretty much instantly anyway
for merc, use coh instead of forti for the life leech. his damage will be largely irrelevant as nova sorc, he needs survivability more than anything else
did you make sure to get a "prayer" merc ? else cure/insight won't combo with it and you're going to have trouble replenishing life
about frostburn, i'm not sure you can get 105 fcr with infy, frosts and 2 soj.
if you want to invest into a solid 2/20 amulet, you can drop a soj for frostburns as it gives a little more mana, but you lose the +1 skill. wouldn't recommend
I had a similar thread with similar questions going and others mentioned Skin of the Flayed one, checked the stash and had a 7% +24 replenish, which are good rolls, but hes pretty durable. Room for socket as well, Havent done a tone of playing with his setup yet but so far so good.
Other mentions included gloom to help with missiles
I wouldnt be surprised if COH is way better but, budget options can be nice too