Hi, your right in your thinking with regards fitting a beacon, under VOSA rules for slow moving vehicles require to have a minimum of one 360 degree orange beacon, there is no maximum and it does not relate to the size or speed of vehicle.
we always run two an all our tractors, along with other led repeaters mainly for doing verge cutting. the main advice is you are very vulnerable on a tractor regardless of size so anything you can do to make yourself more visible the better.
Your thoughts on the pre-manufactured bracket with a din socket is the way to go. I would stick to good old halogen as some of the LED types are not 360 deg coverage and they can sometimes get washed out with sunlight.
Run a 2 core 1.5mm from the battery through a fuse to a relay and switch, you can use one core for the return back to the battery and the other will be the switch wire.
if you need a diagram let me know.
cheapest place to get your bits other than the bracket id CPC, easy to find in google.
any problems drop me a line.