So Jack will be 5 months old on the 25th of this month and he's grown in leaps and bounds. He's almost 6lbs and is as active as ever lol.
One thing he can't get the hang of though is his excitement when he sees other dogs and meets new people. I've been working with him over and over again on this. I take him for many walks, to the park to get used to seeing people around, etc. He's gotten better seeing new people (he still likes to jump all around them & all over my little nieces which I don't like, but he doesn't cry at them anymore) but when he sees other dogs he cries and wags his little tail until he gets to meet them.
Unfortunately, not everyone wants to be his friend like he thinks and he doesn't always get to meet them (some people are weird with their dogs, and/or the dogs are really big and he's still very little) and he throws, almost, a little tantrum. He whimpers and cries so loudly to the point I have to pick him and calm him down and distract him with a treat. He gets so upset when he doesn't receive any interaction. A few weeks ago he met our friends Lab puppy and we had to separate them because the lab is already 25lbs so we let them meet thru the labs crate and Jack barked at him, almost as if he was angry that he was in the crate. He got a bit out of hand and started barking aggressively when he realized the lab wasn't coming out lol.
My mother thinks he should have a sibling

but I'd like to correct the behavior before I bring another puppy into the picture lol. Do you all think puppy classes/obedience training will help him? He's very smart and has learned a bunch of tricks via myself already, I just want to make sure classes like these will really help with his reaction and rejection responses.
I've also just joined some meet up groups on meetup.com for puppy socialization....haven't gone to one yet but again, I think I'd feel much more comfortable if there was a professional opinion on his behavior.
Do you all have any advice and/or recommendations? Thanks so much.