You must always keep a stick when you take your dog on walk. Straydogs may bark and try to approach your puppy but if you show them the stick they'll all run away. straydogs consider you and your dogs as intruders so they may see be wary of you but as they get used to you, they will hardly be any problem. I have hundreds of stray dogs in my area. They live in packs and if they come together they can easily kill a human, forget the puppy. However, they are used to us and never cause any threat. But, for safety I alwas keep a stick with myself. These straydogs now accept us as a member of the pack. They all welcome us when I take my L12 months Labrador on walk.
The bottomline is respect them and they'll respect you and never cause any harm to yourself.
You must supervise what your dog is sniffing. Keep him away from garbage. If he sniffs the road, it's fine and there's no need to cover his mouth with muzzle. Should he chew anything then you must immedietly take it out. Also, let your dog sniff as that's a requirement which you should respect and let him do. However, set a time for him. For example, don't let him sniff for more than 20 seconds. When the time is over, ask him to come on. You should also teach leave it command to your puppy. You can watch youtube videos to see how you can go about it.