I would start out at around 15psi and see how it feels and then lower from there. 10 is more realistic but 15 will give you a good place to start. You'll be fine in 4hi starting out. In my 4runner I go back and forth between 2hi, 4hi, and 4lo the whole time out there, but I can do all that on the fly. I know in my wifes tacoma, I can only go between 2hi and 4hi on the fly.
A good trick for speed, start out in 4hi and once you are moving pretty good and on top of the sand, switch it to 2hi and you can really get some speed.
See you out there!
