Well, hopefully someone more expert will chime in to confirm, but here's what I understand. Given the earlier info is correct, and I believe it is, you have a 10amp and a 20 amp circuit to use back there. About all I know when it comes to this stuff is from Ohm's law, so using this version:
Amps x Volts = Watts
then the one connector supports up to 120 Watts (10 x 12 = 120), and the other up to 240 Watts (20 X 12 = 240).
That means either of the connectors will be more than fine with the lights you're looking at, with a total of 99W. I guess which you use will depend on if you want the lights to only be able to be switched on if the tractor ignition switch is on, or whether you want to be able to turn the lights on even with the tractor ignition off.
As far as switches, there are a plethora of styles, so you may just want to make a stop at a hardware store and browse them - as long as you choose a style that will support the voltage and current. Any switch that handles 12V or more (most any of them), and the current through it. If you put all three lights on one switch, you'd be drawing only 8.5 amps.
99W / 12V = 8.25
If you put the two front on one switch, and the back on a separate then
72W / 12V = 6 and 27W / 12V = 2.5
so, if you wanted the switches to be the same style you'd need to make sure they were 6 amp or more. You won't have any trouble finding switches to well exceed any of these limits.