Wow, sorry to hear about that. I am not a vet but I've had 3 horses with leg injuries of different kinds. My first thing to do after checking for wounds or punctures is to check for warmth -- if you have more warmth than in the other leg, hose it for 20 minutes several times a day. Managing any heat and swelling is an important first step to avoid additional tissue damage to the tendons, ligaments, blood vessels and nerves from the heat/swelling.
Second thing is to check for swelling, as you've done. Depending on where the swelling is, it might be a good idea to wrap the leg if you have the right material and if you know how. If you don't, just do more hosing -- you can cause damage from improperly wrapping so it's best not to do it if you're not sure. It requires Vet wrap or standing wraps, not polos, wrapped over gamgee or quilted or no-bow bandages for cushioning.
Through all this, keep him stalled in deep bedding like you're doing. This allows him to lie down if he wants to, which will help protect the leg. Also, don't wlak him around until you get the vet out tomorrow. If it's something serious, that will of course make it worse.
When mine were injured, the vet prescribed bute for pain but for exams, he wanted to see how they walked without the bute - so you should wait to see what your vet says about pain killers before giving your gelding anything for pain. He may need to do flexion tests and so forth to determine what internal structures have been injured, the bute will mask the pain so well that the vet might not be able to pinpoint what's wrong.
Last but not least, go with your gut. If your gelding is eating and drinking, those are good signs. If he seems to be in a lot of pain and you think something's broken or dislocated, that's an emergency.
I just had one of our geldings, a little younger than yours, come up lame in the left front last week. He was barely weight bearing, and there was a little swellling and a little heat and no obvious wound. We did all of the above, except didn't call the vet since it was the day before Thanksgiving. Over the next 3 days, the swelling pretty much went away and the heat went away; he was less lame. By Saturday he was walking normally and by Monday he was back in the pasture with his buddies. We think he maybe got kicked or twisted it in horseplay. He is one of those horses that is very protective of himself and as long as it hurt, he didn't walk on it. So, we took care of him as if it were a tendon injury and after about 2 days it was clear that it wasn't. (Note: I've had a couple horses with tendon injuries and I know that they can be really bad even if the heat and swelling are very little, so if the swelling and heat increase you have something that needs a vet.)