I assume you'll be learning strip (warm) wax and hot wax.
It's much easier to wax with several inches of wax to dip into and It's tricky to wax when you've only got a little bit of wax left in the pot. Decanting half a pot of wax without making a sticky mess is an artform. You need decide whether to get a small heater that holds just one pot of wax, and maybe try topping up with half a pot of wax at a time or get a big heater which will hold 2 pots of wax so you can top up with a whole new pot and always have a nice deep wax pot.
Wax heaters usually come with a removable insert pot - check. Don't pour wax into a heater without a pot insert.
Warm wax is sold in around 450cc plastic pots, Don't get the 800cc metal pots as these are usually advanced waxing products and you need to practise the basics. Warm wax is personal preference, if you can manage to spread a super thin layer you want a "grippy wax" if you spread thick you need something more gentle. Get a honey wax to start as this is what you'll use in your course. When I trained our trainer got several types of wax for us to try out. The students liked different waxes to the ones the tutors preferred.
If you buy an extra insert pot and plenty of cotton wool pads, some gloves and a big bottle of surgical spirit you can swap a hot wax insert pot with your warm wax pot. Lift your pots out regularly to clean them and always put a sticky pot down onto a couple of wax strips resting on a kitchen plate or ideally a ceramic tile.
You might prefer a digital heater rather than an analogue dial - but all pots have their quirks. Don't worry about brand. My preference is for a sleek design as I find these easier to keep clean. They are tricky to pick up though, I've dropped one before - it was full and hot! The ridged designs with a good handle are safer if you are moving your wax pot around.
