For a taildragge, you want the axle of the main gear to be slightly forward of the leading edge of the wing.
The gear needs to be tall enough to allow the prop to clear the ground.
If you are flying off grass, make the gear tall enough to clear the grass and the wheels need to be larger.
Retracts look great, but they are far more fragile than fixed gear.
Not sure what you are looking for, hope I’m answering the question you are asking.