Hi. I have twin sons who are now 5 and I had major potting training issues with one, but it was not compounded with all the other issues you have. When it came time to start preschool at 3, he was pee trained at home, but not poop. I sent him anyway. He really caught on quickly with the other kids around him and never had an accident. He always just held his bowel movements until he was home. He's very private and won't go with anyone around, even at home, he must close the door and be by himself. I'd just give the preschool a try and see what happens, being in the structure with all the other kids might get him in a better groove. The watch sounds like a good idea, too.
As far as night time goes, keep him in a diaper, the body is just not ready for this, you can ask your doctor, sometimes it can take years and it is NO fault of the child. Good luck.