Sounds to me like you and your dog both need some training. You are situationally alert but you are way too paranoid.
I would be willing to bet that that guy on the bike was totally unaware that you were even there and you scared the crap out of him.
The 2 women walking thing just plain eludes me. Do you honestly think that you should be the only person out walking? In my neighborhood people are out walking all day and half the night too.
As far as your dog altering his behavior and barking at people while on the leash, that behavior is not good. You will have problems later if you allow this to continue. You need to seek out some dog training for you both. Your dog and you need to learn appropriate behavior in social situations. Performing watch/guard dog duties in the house is desired but not out in public.