Get a thermometer! ASAP. In a pinch, you can use the human ones, but remember to hold them really tightly as the horse can actually pull them into his body. So make sure you don't get vaseline on your hands or on the back of the thermometer where you are holding it. You want to invest in termometer that you can hook a baling twine on the back so you can't loose it. I think Jeffers sells 5 second thermometers that are really nice.
I'm not sure why you waited so long for the vet? Stocking up just means some swelling which quickly disappears with work. There should be no heat, just some slight fluid buildup and it should leave a dent if you push on it.
What you are describing, is oozing sores, and very firm swelling that does not dent, means you have a much worse problem going on. I'm glad the vet is coming out.
Cellulitis, especially if it is spreading may mean you need IV antibiotics.
Do you have vet wrap, banadages, betadine, peroxide? Some of those things are an absolutely must for dealing with horses.
I once saw a horse almost bleed to death because the barn he was at did not have a first aid kit. If you or someone else gets injured while at the barn, that first aid kit might come in handy as well. It's something that it is always a good idea to have.
Ranitidine is another product that is useful - you never know when a horse is going to have ulcers and need some! You can pick up the people stuff over the counter and give it to your horse in a pinch.
I like to keep antibiotics on hand as well, banamine, benadryl, bute, and syringes of different sizes, and needles. I'm sure others can add more...