Hey ampnaman
Thanks for trying Demon out, and I'm glad you're enjoying it.
Early relic wraiths can definitely be a bit of a bother: since these are player ghosts, they can have access to some nasty abilities from starting packages early on. If you're not feeling confident, you can skip searching corpses, or pick up the Enemy Sense relic upgrade (which will tell you which corpses are going to spawn enemies or become wraiths) and get the goodies without the danger.
The pair of ghouls in Tower: 1 & 1/2 are toughies, as can be some groups of blaster enemies. One tip I can give that definitely applies to ghouls, and often other troublesome groups: look for opportunities to use recruitment mechanics to break up things a bit. For example, Ghouls are recruited by joining up with one and helping it rampage around the level. If you run into that pack of 2 ghouls, you can start a link with one and it will help you kill the other.
Even if you ultimately fail the capture attempt, you get to fight both ghouls separately instead of together. Look for similar opportunities in other troublesome groups: they are not always present, but more often than not they are.
Yeah, the Currency/credits system needs a bit of tuning. I'm in the middle of some experiments with combat at the moment, but this is probably next on my list since it's sort of bugging me too.
Uniques're definitely difficult to recruit, though they will be a little easier in the combat experiment build since damage across the board is up a little.
As for Actaeon vs. Artemis, that depends on who you ask.
In some circles, Actaeon is widely regarded to be the best choice due to the abilities he provides when used with Fuse Demon, Revelation, or Transpose Soul.
I'm still working on it, so more content will be coming. There's already 23 floors to the main Tower and a smattering of side-dungeons to explore, so you've got plenty to keep you busy depending on how far you've gotten so far.
Good luck in the Tower, and thanks for the feedback.