Fifth Wheel Towing Limit and Axle Ratio 3.73 vs 4.10

I would get the 4.10 ratio if this is mainly a tow rig. If you will drive it around empty every day when not towing then probably the 3.73 would be better.
You absolutely want the limited slip. They make a big difference in muddy, snow, generally low traction conditions. There really isn't much of a downside with a properly functioning limited slip.
I'm glad you've read up on the 6.0. We had two at work. Even when they weren't in the shop they were loud, hard to start, and handled badly.