I remade the mage I posted above and am on level 5 with him (Going Rogue difficulty). I dropped Golemancy for Ley Walker and I don't regret it. Somehow my level 2 shops had two stupidly good mage items, one of which I managed to be able to buy once I cleared a few rooms of level 5, which is called "Orb of Nothing" and has amazing stats. Like 2 mana regen, 30 magic power, 10 of the core intelligence stat (whatever they call it), and some armor. Between gear, Ley Walker and Blood Mage I generally have enough mana to cast anything on demand, and even be somewhat wasteful if I need to be.
As to what I'm spending that mana on, Promethean Magic friggin' owns as soon as you get Explosive Rune. You can plant the rune anywhere in your line of sight and the damage is hilarious. Every Monster Zoo I've done from floors 2-5 has been an utter joke with not a single monster getting out of the doorway to the room - the first Explosive Rune will usually kill 4-5 monsters on turn 1, and Blood Mage returns magic per kill. All I need to do is just chain cast it because I'm getting more mana back than I'm spending from Blood Mage. The only downside I've seen is that if you plant a rune over a splattered floor tile (where something died and the corpse disappeared), you can't see it, and you can trigger your own runes. I almost died the first time I obliterated a Monster Zoo because after everything died, I tried to walk into the room and set off two in a row that were hidden under goop that never got set off.
While I wouldn't mind having the Golemancy wall manipulation skills still, the whelpling from Promethean Magic is quite a strong pet and you can use it just like the Golemancy ones if you're a Vampire, as they will never turn on you if you hit them. The whelping has a ton of health, and you can even eat the corpse once it dies if you need to.
What I am finding is the biggest obstacle are traps. On the hardest setting these things are damn dangerous and more than once have almost killed me outright. I'm quite concerned that I'm not going to be able to handle the deep floors if I get there because I can't disarm anything really unless I find some trap-related gear. I found the Vampire Hunter's hat but it seems the stat that determines trap vision and the one that determines trap disarming are separate so I still can't disarm any traps whatsoever safely.