2.5 year old - not sure if we should continue?

Hi, I've been lurking on this thread for a while and decided to make a post as I am truly confused.

We started with the Oh Crap method with my 2.5 year old son over the long weekend. He's very verbal and pretty smart. We did the naked method, had one pee where we managed to get him on the toilet in time on Friday, and really nothing since. I get the sense he does not want to pee or poop in the potty at all. After we started potty training, he did not poop for two days until we finally put pull-ups back on. And on Saturday, he started peeing a little, got it on his foot, freaked out, and stopped peeing and would not keep peeing in the potty. I think he withheld it.

I will say - he was very proud of himself after he peed in the potty, and he enjoyed emptying it into the toilet.

As a result, we just laid off a little on Sunday and kind of since then. I think I put too much pressure on him when we started on Friday.

What we're doing now is timed sittings with us or our nanny during the day. We got him the Ms Rachel book and toy (Bean has his own potty!) and that seems to have made it more exciting to sit. He also has a Tonies box that we only use during potty time. These things have all helped over the last day or so, but we are still not getting anything in the potty.

For context, he hates mess as a kid (doesn't like fingerpainting, gets upset if he spills water on himself) so this bodily fluid stuff is not really up his alley.

Issues I don't really know how to understand:

1. We try to have him be naked or even just in his pull ups. He keeps yelling that he wants to wear pants. I think he is associating not wearing pants with using the potty, and I don't think he wants to go on the potty.

2. He is happy to sit on the potty with pants on. He protests a little when we do the timed sits.

3. How do we handle the withholding? Should we continue? Should we stop?

4. Are the timed sittings really worthwhile? I think he understands the concept but I don't know how to remove the fear of peeing / pooping, and I am not sure we are going to clear that up until he actually does it in the potty and sees it's not scary, and I don't think we are going to actually get anything in the potty with the timed sittings. I think he is ready, on many levels. But I don't really know how to go about this when I sense that he is withholding, and I'm not sure how to change that.