memmo is my favorite for runs, since you can do about 10 runs in 20 minutes!
What I do is, I do tower run in act I in order to try to get keys/runes, and also since the "experience enhancer" can be found easily in black marsh.
After this I go to act V (with the experience blob above me) and enter teleport nr 1. Go north and south and you will be able to kill 2 unique monsters and gain quite some experience.
After this, I go and do a memmo run. All this takes 5 minutes or so, and covers A. MF'ing, B. Key hunting, C, Rune hunting and D. Experience boosting. I can do 12 such runs an hour.
As for the firewall question...well my sorc is a frozen orb/meteor...and it requires skill, or a good tank in front of you, not to be KIA when comes to big groups of monsters. Firewall has been nerfed.
Mephisto is a constant source of decent drops to get you started (and even more with enough perseverance). It sure was, still is, and will be a great item provider through the Ladder seasons :thumbsup: !