I do go to dog parks, and have for years, but I'm picky about which ones, and I try to go when we coordinate to meet up with other owners and dogs we know from our training group and the trainer's socialization field.
1. If your park has double-gate access, I strongly prefer unclipping the leash in that area, then letting the dog into the park unleashed. A leashed dog confronted with a bunch of unleashed dogs is more likely to react, IMHO. The gate is the most dangerous point of the dog park. If my DH and I are together, one of us often goes in to shoo the other dogs away from the gate to make some space for ours to enter. Everyone does this at our socialization field too if people get there late--whoever is closest to the gate will shoo the gate-guarders away from it (no matter whose they are) to let the new arrivals come in peacefully.
2. This is a vocal breed. We have 16 of GSDs that play together at our socialization field, they all have different play barks, and some of the girls yap at each other like noisy teen-agers. They're simply loud. There may be 20-30 other dogs on the field, but the GSDs make more noise than all of them.
3. Hackles can go up during play, as a matter of excitement. It's not necessarily
inappropriate--it depends on lots of other body language. That said, there's nothing
wrong with asking your dog to sit and calm down before being released to play. Play as a reward is a great
4. Kudos for not allowing him to bully the insecure dog!
Our group at the DP would be supportive of you working with him to stop that--and frankly would intervene to stop him if you didn't. This is the advantage of going with a group I know and trust from the training field.
5. Now for the bad news: I think taking an intact dog into a dog park is bad form. Sorry -- it just is. A lot of parks forbid it. That doesn't mean tons of people don't do it, but the fights I've seen at dog parks often seem to involve intact males.