Is there something else I could do to discourage him jumping up on everybody he meets? Should I just avoid these little meet and greets altogether until he's a bit more trained?
No, it would actually be better if you USED those times as training opportunities. It's hard to train him not to jump on people if he's not allowed to greet people, but you need to manage him so he's not able to jump on them.
My dogs get very excited when people come over, even though they're adults at 7 and 4, because we don't have guests that often. I keep them on leash until they calm down, then I'll drop the leashes and let them drag them until I'm sure they won't jump, and only then do I take the leashes off.
If you're out and about and people approach, train him to sit. If he breaks the sit, stop until he sits again. Have the people back away if necessary, so his behavior controls whether or not he gets to meet them. Calm polite behavior means people continue approaching, out of control jumping means he doesn't get to meet them.
As far as greeting you when you come home, that was an issue I struggle with for a LONG time! My dogs were so happy to see me that it seemed like nothing would work to stop it. One thing I've tried that is helping is to not come in if there are heads sticking through the crack as I open the door. They do know "go" (in the direction I point) and I've taught them to back up with the "back" command, so I use those too. I start to open the door and then close it again as many times as necessary to get them to back away from the door until I can get through it.
I also had a bag of treats in the car, and I'd grab a few before I got out, and as I opened the door I'd toss them into the entry, over the dogs' heads while I walked in. Whoever wanted them had to move the fastest!
Also, I noticed that if I came and went a couple of times they were less excited each time, so whatever method I was working on, I might do it 2 or 3 times in a row. It took awhile, but they are MUCH better, and now I can almost always get in the house unmolested. Halo is the worst jumper (she's the younger one), and now she'll often move away from the door and go find a ball as I'm coming in the house, and she'll run happy circles through the kitchen, dining room, living room, and back to the entry, with her ball in her mouth instead of jumping all over me. I greet them when they've got all four feet on the floor.