What if it happens on the 3rd floor? (if it can, I don't even know)
Check the picture, it
was on the third floor.
If you want a challenge, just play Angel of Berserk. That'll drop you a few times, I assure you. I just recently managed to get to level 10, and that was only due to my finding the butcher's cleaver on level 2.
Angel of Marksmanship is actually relatively doable. It's annoying when you find a combat shotgun on level three and the unique rocket launcher a couple stairs later, but choices are made easy for you.
Lately, I've been plugging my first points into reloader and SoaB. I'll wait for shottyman until I actually get something that really needs it (I.E., the double-barreled death-dealer), unless I'm looking into other areas. Since there seems to be a pretty even dispute between shotguns and chainguns, I've tried my luck at chainguns a couple times. As such, I'll plug points into eagle eye so I can actually hit something.
Fenrir, if you plan on keeping up the dodgy lifestyle, I really do suggest shooting for shottyman. Reloading on the run lets you constantly keep moving. And the double-barrel can shove out quite a nice amount of lead, especially if you've got the speed to get up-close and personal with the baddies before you let fly. Plus, the necessary reloader points will help you out if you decide to switch over to explosives later on (there seemed to be more rockets than shells lying around last time I was in hell).
I don't know if I'll ever really get the hang of chainguns... Sure, the points open up the way to nice plasma gun handling later on, but there's just something innately satisfying with blowing a demon away using a shotgun.