1. My amazon is a pretty quiet guy overall, and even quieter in public. Being outside their comfort zone/territory makes most parrots not want to draw too much attention to themselves. I mean, you never know if a tiger or anaconda is lurking nearby while out with your human

Kiwi loves the car, bus, train... He just loves being in anything that moves and makes all kind of interesting and hilarious squeals of joy!
2. I use a pak-o-bird when we go out, but my bird is also potty trained. It is possible to potty train a bird and IMO I don't get why more people don't It's no more difficult than housebreaking any other pet. Focus on elimination communication (i.e. them letting you know when they have to go and setting up designated areas) rather than training them to hold it and only go on command (which can lead to serious medical issues).
3. NO! Stranger can say hello and talk to Kiwi, but no touching. He's an animal, he can inflict hard bites and I don't want to be sued or have him taken away and killed by animal control like they will dogs who bite because he bit some idiot and they complained he was a 'vicious animal'. Again, I use the pak-o-bird when we go out, which completely eliminates the risk of him biting someone yet still allows people to say hello and interact SAFELY with him.
These are pricey, but one of the best investments a bird owner can make when it comes to taking their birds out with them. Safe, secure and eliminate most issues of taking a parrot into public. The small "birdie go go" pack may be suitable for your needs with a bird the size of a conure:
https://www.celltei.com/BIRDS-by-species/Small-conures.html
(I believe a sun is a small conure, but you can look around at larger sizes if needed)