You DON'T need three upper body days (especially if you're already out of proportion)! If anything you could flick that around and do 3 lower body sessions, since you sound like you need it; and you'd also get more growth in your upper body by training your legs that often.
However, this is what I recommend you do:
Monday - Lower Body/Abs
Tuesday - Upper Body
Thursday - Lower Body/Abs
Friday - Upper Body
You should be focussing on the mulitjoint, compound movements (i.e. powercleans, squat, deadlift, bent over row, pull-ups, bench press, military press, dips, calf raises (only isolation exercise I would recommend), etc.) to get the most out of your sessions (your bicep, triceps, lateral delts, and rear delts get used in those exercises, which is why there is no need for isolation exercises).
Yes, when you train something that you don't normally train or have had a break from, after the first few sessions you WILL feel DOMS. However, you can EASE into the sessions (i.e. with lower body you don't have to go straight into lifting; do a few light warm-ups sets first, and then build up with your weights).
STANDING for however long, regardless of sore legs, should not be an issue. You're NOT moving. It's not like you're spending 10-12+ hours standing/walking/running on TOP of your training! Despite that, your body adapts, and DOMS becomes less or disappears after a while.