Glad to see this post as I just finished my first weekend camping with our new 5th wheel and I was curious about the "how far to lower landing gear" part of this.
I stacked 3 2x6's under each leg and pulled the pin till the leg hit the boards, then raised the camper off of the truck - basically the only "extension" of the front legs was enough to raise it off of the truck, so to level, if I needed to lower the front I guess I was in trouble.
Mine has the 4 point auto-level, so once everything was disconnected and the truck pulled away, I let it do it's thing - not sure what it would have done if it had needed to lower the front, so I guess it's a better practice to lower the front legs a few inches before "pulling the pin"..... I also plan to get a couple of 6"x6" blocks to use instead of stacking the 2x6's. (yes, they are about a foot long)