When the wand hits a modifier it reads to the right, picking up any more modifiers until it hits the next spell. So you want to put your modifiers on the left, with the best modifiers last, so they trigger on the maximum number of clicks.
My best random wand so far, once I cleaned up the spell order, was bifurcated cast and three bouncing sparks with trigger, basically a bullet hell wand that filled any enclosed space with bouncing sparks. Unlike the sawblades which also bounce, the sparks don't damage you, so you can just fill a room with sparks and run through it. Another really good spell is glowing lance, which passes through any loose material. Really good in snow and coal heavy areas, you can hide behind them and kill people through the powder.
Favorite death so far, I got the electric perk which electrifies any metal you're touching, accidentally landed on one of those sea-mines. It blew up and threw me across the cave, directly into an oil barrel, which also blew up. I got alley-ooped.
And yeah, the whole map is one instance. THere's a lot more than just the sequence of levels passing through holy mountain. If you find chaotic polymorphine (remember you can right click to squirt instead of throwing it) you can fly over the cliff to the right, there's a floating island with an orb and an altar, and even further to the right there's a desert with a pyramid dungeon. Underground there's a lava field on the right which I haven't managed to cross yet, don't know what's on the other side. To the left of the dungeon there seems to be a side dungeon that goes all the way to the bottom with no holy mountain transitions.