Just a few things if your new to climbers if I may; Get used to it, pre season go find a tree and go up a few feet, and out how well the modle you buy settles in, how the seat adjusts, and setting up the harness strap. Get used to adjusting the starting angle. Avoid smooth bark trees. Also fix your drop rope so it doesn't get in the bite.
Personaly I like the foot platform as level as can be, if it's slightly down angled - can't get comfortable. Around 17' for me is good, sometimes near 20' Over 25' - might as well piss myself.