The normal age for walking has been moved back since kids have been sleeping on their backs. My ped says that walking at 18 months is still within the norm these days. Walking at 12 months is now considered early where it used to be more the norm. So I wouldn't be concerned about that.
We did sign language with my kids, but they developed language very differently. My daughter used her signs regularly, but really wasn't verbal until more like 20 months. She's still shy about talking to others but has strong language skills at 3. I have an uncle that is an orthopedic surgeon and my grandmother always talks about how he never needed to talk since he had 2 older brothers and really didn't until he was 3 - they thought he couldn't hear, but he got along ok without talking so he didn't. My son started with signs, but moved past them quickly. He just said everything early. He'd learn words and then learn signs to match them afterwards. He also picked up on pronouns and sentences quickly and by 18 months he was basically talking in full sentences that most people could understand.
Both of mine are picky about being dirty. I just make sure to have lots of wipies with me any where we go and they get the majority of mess off to keep them happy until it's time for a full bath. There are tons of different textures at the park and some kids are sensitive to that. Just try to expose him to the textures by places a couple wood chips on his hand and then let him choose to explore or not. Swinging is also a different sensation. Let him try and then let him choose to stop too. Maybe try a small slide - sit behind him and hold him and go with him at first to help him adjust to it.
All kids learn differently. Watching others play is one style of learning - observing. In time he'll develop an interest in interacting more with the environment. For now, let him process the many new sights, sounds and smells in his own way.
14 months is really early for interactive play. I wouldn't expect that most 14 month olds would really be playing with other kids unless they were older and the older child was initiating the interaction. Kids that age aren't necessarily even parallel playing yet (playing the same thing next to each other but not really interacting). From my experience, when they have a close sibling, they do develop play skills a bit earlier as they have a built in playmate 24/7, but that also depends on their personalities.
Hope that helps a bit - it really sounds like he's doing just fine from your description.