JR, all good questions I will address them one at a time.
1) "It's my understanding that it starts using 12 volts through the coil, but run at 6 volts - do help save the points."
With a 12 volt tractor using a 6 volt coil plus external ballast resistor, that's primarily to improve cold weather starting as full unballasted voltage is on the 6 volt coil ONLY while cranking (cuz ballast is bypassed), afterwhich its 6 volts on a 6 volt rated coil as the ballast drops approximately 6 volts. Its NOT so much to save points, although sure if 12 volts were constantly applied to a 6 volt coil the points would burn up prematurtely...........THE SYSTEM IS MOSTLY TO IMPROVE COLD WEATHER STARTING.............
2) With the electronic ignition - I'm guessing there's no need for this:
NOT necessarily so. The elec switch simply replaces the mechanical points switching, the rest is still the same. Even if points or an elec switch is used the 6/12 system still improves cold weather starting, although sure, the tractor still runs fine if you toss the ballast and use a full true 12 volt coil, regardless if points or an elec switch is used.
3) What do other people do here? I've been googling, but it's confusing me.
SOME toss the ballast and use a new full true 12 volt coil SOME retain the old 6 volt coil and ballast bypass system which can improve cold weather starting SOME use an after market so called high energy or high voltage 12 volt coil provided the elec switch can handle its current
4) Can I just use any 12 volt coil in place of the old one, and bypass the resistor completely? Am I overthinking this?
YES you can toss the ballast and bypass system and use a new full true 12 volt rated coil.
5) I have my reason for wanting to change the coil anyways - but I'm just not sure what to do.
THATS YOUR CHOICE NOT OURS If you want to change the coil anyway GO FOR IT.
REGARDLESS if points or elec switch is used you can still EITHER use a 6 volt coil plus ballast and bypass orrrrrrrrrrrr a new full true 12 volt rated coil of your choice which the elec switch can handle.
Others may add to this, I'm sure I forgot something. There are advantages and disadvantages either way but I'm NOT going into all that, just trying to answer your questions