MF165 Coolant Leak / Overheating

New to tractor ownership and looking for advice (MF165 Perkins gas engine).

I've had this tractor for several months and this is the first problem I've had with it - and I'd like to figure out how to diagnose the problem and and/or confirm I'm not going to do damage by running it.

This is what happened. Sunday evening I use the tractor with a back blade to start plowing snow on a 3/4 mile driveway. Tractor works great, driveway gets half cleared but I run out of time and end up leaving it near the end of the driveway to have dinner with the neighbors. When I return 2-3 hours later the tractor won't start (no sound at all). I walk home.

The next morning the tractor starts fine and I continue clearing snow, but within 10 minutes I notice coolant pouring out on the right side. I immediately shut down, but I can't tell precisely where it was coming from, although I believe it seemed to have boiled over and drained from the overflow hose that attaches near the radiator cap (with some being sucked in / spattered by fan). Top radiator hose felt warm/hot, but bottom hose cool.

Left tractor where it was and I subsequently topped up coolant and replaced the radiator cap with new 7lb. Drove tractor home next day in 2 short 5-10 minute rides so as not to overheat anything and parked in barn (no problems - although I wasn't plowing, just driving). Oil appears fine. What would cause this? For what it's worth, I have never flushed / replaced the coolant since I owned it... Also, I don't think the temp gauge works.

My best guesses in no particular order:
Clogged radiator
Stuck thermostat
Bad water pump

What would you look at / replace? How cautious should I be in using it so as not to cause any damage to the tractor? Also, what coolant should I be using?
Any advice appreciated.
Thanks!

It certainly puked a lot of coolant. I would remove the thermostat and refill the radiator and look for a leak. You should be able to see if the coolant is circulating with the thermostat out.
When you drove it home did you notice any more loss of coolant?

Obviously the leak is job 1. Until you get the leak fixed you can't go much farther.

After that I'd get one of those cheap IR temperature guns and run the tractor for a while with the radiator cap off. The water will be calm in the radiator while the thermostat is closed, but show a definite flow if it opens and the water pump is working. Then shoot the temperature of the upper and lower radiator hoses. If you get a 20 degree drop your radiator is working.

I have a 30B with a continental gas engine and a 180 degree thermostat. With the tractor up to temperature I see about 230 degrees on the metal thermostat housing, 185 on the upper hose a few inches away from the metal of the engine and 160 degrees on the lower hose.

you did not give an antifreeze strength nor how cold it was. it may have gelled up from being week solution. pretty obvious if lower rad is cold and top is hot due to water pump not pumping coolant.