If you have an efi engine, turning the idle up will help reduce stalling when trying to crawl over obstacles just off idle.
If you have A/C, turning it on will put drag on your engine, allowing to go slower for descending a hill, or when dropping off of ledges, though not as useful when tires are larger than gearing.
As far as what gears to run in, IME, 2nd and 3rd low range are the most useful on the trail in the rocks, you can usually take off in 2nd(assuming you are running tires with correct gear size) and rarely need more speed through smooth terrain than 3rd, as well as 3rd usually having enough torque to slow you down quickly for any surprise change in terrain or opposing traffic, etc, then using 1st low for crawling over obstacles. Once you have few hundred hours of seat time on different terrain with your rig's set up and driving style, you will have a better idea of what gearing works best.
For descents you should avoid trying to change gears, the momentary depression of the clutch can easily result in a gain of unsafe speed,
A bar wont really help with axle wrap for hill climbs and likely result in breaking something. The best way to address the issue of axle wrap for your purpose is through lockers and dual transfer cases, so you can climb the hill at a slower speed maintaining traction, and not have to rely on speed alone to get to climb a hill.
