Front to back:
I try to level the main support beam (that runs from pivot pin to 3PH) parallel to the ground. I find if the 3PH part of the rake is Lower, it tends to hop and skip when it hits rocks, ruts or dips. If the 3PH end is higher than the rear, then I find it likes to dig in. That's just my un-scientific and very general observations.
Depends on how aggressive you want it to bite.
Side-to-side height is pretty intuitive. if you want crown a driveway, set it lower on one side. if you want to pull more material the center, angle it.
I've only got a few hours on my gauge wheels, so far, as a mere-fledgling, I am finding that you will probably operate the gauge wheels for the rake anywhere between Zero inches and plus or minus 2". Zero is when the Rake tines and wheels are even with each other. 2" up is when the gauge wheels are 2 inches higher off the ground, which would give you 2" of "cut".
When finish grading dirt for grass seed, I ran the gauge wheels about 1 inch up, meaning the rake could dig in 1 full inch, and that gave good enough cutting it dirt, without getting too deep. it also did some filling in small low spots.
Running the Gauge wheels at Zero inches sounds non-productive at first, but, I found it good for raking trash and small limbs, without cutting into the dirt. Without gauge wheels I tended to end up with a pile of trash and dirt, all mixed together, and scarred-up gouged ground left behind.
If you have an existing pile of dirt that you want to spread evenly, then you can raise the rake a bit (Lower the wheels so the rake tines are off the ground a little) , and pull the pile which will allow a measured amount of dirt to slip out underneath.
I haven't used it on any gravel yet, but if i did, and was smoothing a driveway, I think I'd start with the wheels UP by 1 inch, allowing the rake no more than 1 inch of "dig" , try that, then adjust from there.
Hope this helps a little bit, it's something you may need to play with, to see what works for each situation.
One thing is for sure, the gauge wheels are like being on auto-pilot compared to not having them.
Good Luck