Run bosses on p1. It's just fine.
I still run Mephisto from time to time even though he's given me pretty much everything he can, but he can still surprise you. I got an extremely good +2 Arkaine's valor the other day.
For pindle, teleport right through to the temple. Pindle and his dudes aren't CI, whereas the guys outside are.
Run AT. It's amazing for a blizzard sorc.
The best base for any merc armor is an ebugged <anything elite> pretty much. You find an ethereal elite armor with no holes, and not superior. You add sockets to it with the cube recipe tal+thul+ptopaz. If it gets 3 sockets, duress or treachery are good options. I prefer treachery. If it gets 4 sockets, stone is a good option. On the high end of course there's fortitude, but I don't think you need to worry about that yet. If it gets 1 socket you throw it away. If it gets 2 sockets you could put smoke in it I suppose, if you haven't found something better. Or you could save it to make prudence for a melee player character instead.
Insight is brilliant. There's no reason to abandon insight for anything other than infinity, pretty much.
edit: for a lowish geared dual-tree build tankability is more important than damage on a merc, so I have to say of all the options I like ebug stone the best, rather than duress or even treachery. A defiance merc with ebug stone is nigh on indestructible to physical attacks. Add a tal's helm to top off resists and add 10% life leech, and you're laughing.
My merc now got a brand new ebug stone on him
Felt bad using the runes, but it turned out to be a 3575def hellforge ethereal armor.
This also maxed his resistances, so hopefully he won't be dieing
Also managed to run pindle now, thats where i got the plate.. After 20 runs, all i got was that plate lol, and 4 full rejuvpotions.. Not one unique :o