Thanks for sharing. Yeah I worry if I get nervous that the church would reject me like I'm an outsider. I've heard about churches that are a little judgemental and dismissive of single adults, like family based churches. You're right though that people will be mostly focused on the service and probably aren't thinking of people in the pews. Dress code is also a concern of mine since I don't have anything nice to wear.
It really depends on the denomination. My former church that I attended for just over a decade, was pretty big on appearance. They really encouraged us to dress up for church, most of the guys wore suits and ties, as I did. They certainly wouldn't turn away anyone not dressed like that though. But I felt they were a bit too big on outward appearance. They would take this verse or that and then come up with rules like women can't wear jewelry or pants ever, or men can't wear beards, etc.
I never really agreed with all of that, and after I left I started to see it isn't really true. They were taking a lot of the verses out of context. I don't know that they did it necessarily, but it always seemed like a reason to be one more thing that people would use to look at others as unspiritual because they didn't follow this or that teaching.
The church I go to now is casual. Some people come in suits and ties, but most people don't. Some even wear T-shirts and jeans or shorts to church, and nobody really cares. I actually donated my suits when I left my old church because they didn't fit me that well. Now I usually just wear jeans or khakis and a long sleeve shirt to church. It's comfortable and the focus isn't on having to get dressed up. I was kind of tired of having to dress up all the time for church to be honest at my old one.
After I left my old church, I didn't attend any services at all for a little over a year and a half. I watched services from a few churches around here online to see what they were like, and sometimes I'd watch services online from my old church. I've just last month gotten into attending a church regularly again.
As for the being a single adult, it's not really a big deal. That was what worried me too is that I wouldn't fit in being single. There are families and couples at my new church but there are several single people around me age too. Same at my old church, although most of the singles there have gotten married or engaged lately. But yeah, being a single adult at church is really not that uncommon. I'd say it's more common for Christians to marry than stay single past a certain age, but there are plenty that aren't.