Generally speaking, you only will want to engage the 4 wheel drive if the conditions are slippery enough to warrant it. If the roads are plowed and fairly dry, leave it in 2wd. Otherwise, you can damage the transfer case. However, you can go ahead and leave the hubs locked, that will not hurt anything. That way, should you need to engage the 4wd, you will only need to lock the transfer case itself. You may need to back out of the throttle bit if you have to shift from 2wd to 4wd on the fly. Driving it in 4wd on snow covered roads will not be an issue. As far as speed, in high range, there really isn't a limit, other than what would be a safe speed for conditions. In low range, you would want to watch the speed as you could over rev the engine. Unless you're moving a heavy load or perhaps pulling a stick vehicle out, you won't need to use low range.
