For cold feet: Ariat Bromonts, merino wool socks - I like the Tredstep winter socks and Smartwool best, but any of the Smartwool knockoffs on Amazon work the same - plus the air-activated insole-shaped toe warmers. I can manage a full day at the barn even with the digits in the teens with that combo, and I run cold.
Hands are hard but I swear by the Roeckl Weldon gloves, and put hand warmers in your pockets so you can stuff your hands in there to warm up during walk breaks.
A little fleece headband to cover your ears, like bikers wear, helps a lot too.
Also, trust us when we say you NEED a big giant barn parka to wear while not riding, and that it will be so smelly and gross it will be worn for no other purpose. You can usually pick one up at TJ Maxx or the Macy’s sale section for $100ish, especially this weekend.