You say that you've built two 250's and two 450's already, so would think you have some good experience from those. My advice is for someone thats not sure of what they are doing. If thats not you then i apologies.
We can give you some settings, but as Rdsok said its different from Heli to Heli. I would get yourself down to the club you were talking about and let them help you set it up. A 500 is not a toy to just "Rev up" and see what happens. I would hate to hear you have injured yourself with it because the setting were not right.
Read all the build threads on here and watch all the videos. Tony has made a lot of videos on set up of helis and the DX6i.
To answer your last question though,
Travel adj (shouldn't need to touch it)
Sub trims are there to get your servos at 90* once you have mechanically got them as close to 90* as possible.
Swash mix i think default is 60% on all which should be fine, then you just have to know if its - or +
Stand behind the heli and and then move the cyclic stick to the left. If the swash tilts to the left its good. If it tilts to the right, its backwards, so change the Ail Swash mix from Neg to Pos or vice versa.
Do the same for Elevator. Stick forward Swash tilts forward.
Pitch, move throttle stick up (motor unplugged) swash should rise (all servos rise together) Stick down, swash down.
Revo mix (Don't touch)
Tony has one of those gyros so i'll let him explain that one.
Gyro gain on the TX should start at 60% and see how it handles (should be done at the Club with a competent pilot)
Hope this helps in some way
