Not totally sure on this, but I'm not sure the transmission is synchronized in first gear. You probably do need to be almost stopped for that.
The red push-pull switch could be any number of things. Four way flashers comes to mind.
On your two speed axle, if you're running empty I wouldn't bother split shifting it. Just leave it in high. Loaded, you could either split shift it or else just run it through the gears in low, then put it into high after you're in fourth. This would depend on how heavy your load is and how the truck handles it. You'll get the feel for it after you've driven it some.
I'm sure others with more knowledge than I will be along to answer your other questions.
