OP, it sounds like you're overwhelmed and like you have some expectations for your DS that might be too low and others that might be too high. (I can only imagine having five sons! I have two sons and one on the way, and I feel completely overwhelmed myself sometimes).
As others have said, he shouldn't be in pull ups starting school. It does sound like the daytime pull ups are more of a power struggle. Have you called the ERIC helpline? They are experts and can be really helpful.
OTOH, accidents at night are really no big deal, as night dryness is hormonal and not something he can control. I know for a fact several boys in my DS's class were still in pullups at nighttime at the end of the Reception year. If you are giving reward/punishment for the nighttime dryness/accidents too, maybe that contributes to him feeling it's all too much?
Finding it hard to go in and not joining in with carpet time in the first week of Reception are totally normal. Some children will be doing it, some won't, and of the ones that are doing it, some will have wobbles later in the year. Once he's made a few friends he might find the social/emotional stuff easier, and he has had literally a few days to do that so far. Try not to sweat this yet and give him as much reassurance as he needs at the start of the day. Some kids in my DS's class were allowed to bring in a comfort blanket or cuddly toy from home in the first time to help with dropping off, would that be possble/help? (Probably not the dummy though)
As for writing, again there is such a range of normal at the very start of Reception. Mine could only do the first letter of his name at that point. By April he was able to write a short, badly spelled sentence and his teacher said he wasn't likely to meet the EYFS standards by the end of the year. However, it just clicked for him after that, and he did meet the standards and got a glowing report.
Writing will obviously come later on for your DS, once he's more settled and better able to concentrate. How are his fine motor skills otherwise? Mine did dough disco instead of writing at school for a while, which did seem to help.
I really hope it all improves for you and your DS.