General

Dumb question, but do you have to do the prereqs again to fight Krexel if you did them before the change?

Well, with my 52k range and 53% boss(idk how i have that much honestly, my staff only gives 30%), I'm able to do zakum, hilla, ht, all the showa town bosses,pianus, pap.
I feel like there's more that i'm missing though

If you can manage to get a bit more boss damage, it'd be a lot easier to boss and would allow you to go for bigger bosses. The only real problem is HP. If you have a potion pot, then you have no worries when it comes to getting seduced at CZak or HT and such.

You can probably take out a boss like czak with a decent group. I suck at hardcore bosses because I'm a noob and lag a lot so I can't give you the best advice xP.

You can solo krexel like the above said. It gives decent exp and there is a quest that gives 7.5m a day for killing it. If you do it all week that is 50m a week for like, a few minutes a day? Especially since it's so easy to get to with spinel being in most major towns. I personally haven't done the prequests yet but once I do I'm going to krexel daily. For money making, we don't really have that many options. Most profitable bosses require insane levels of funding. You could do dimension pq and try to kill Hillas pet. Doing your daily 10 DI's could get you a few Dimension gloves and high quality dimension gloves every 2 or so days. Then you could sell the normal ones for 15m and the high quality ones for 75.
Ahh, the dilemma of the decently funded, but not godly. We can't solo any profitable bosses, but we aren't unfunded at the same time. So what is there to do? Not that much. Most bosses are too easy, and the ones that aren't are too hard.