You're scaring me because I also have a touchy child who does not like change! We're still in a crib, and boy do I dread the BBB!
Hopefully mamas who have been there/done that will help you. I'm just going to address the sleeping bit, ok?
Obviously, he's OT at this point so that is just making the adjustment to the bed harder. I think a lot of what you're seeing now isn't a problem adjusting to the bed so much as being totally off his sleep now from the initial lack of adjustment so that sleep is really hard for him.
Touchy kids also tend to be very emotionally savvy, and can read us like a book. I am a chronic headache sufferer, and my son ALWAYS knows when I have a h/a, even when I try to act normal. So I suspect your son is reading your anxiety about this (and rightly place anxiety!) and it is contributing to his acting up.
I think I'd try a GW technique -- going very slow, with you staying by his side until he falls asleep for the first 3 days. But I'm wondering if there's any chance your DH could do the GW instead of you? At least at bedtime? That might help take some of the tension out of the moment. If that's not possible, then tell yourself that 2 weeks of consistent behavior changes most sleep problems, and so that gives you plenty of time before the baby gets here. If you can take some of the time pressure out of it, I think it will help you feel calmer and then it will help your son feel calmer.
Imagine him in his situation: he knows a baby is coming (its probably pretty obvious by now!
), but he has NO idea what that means in terms of his life. He's also in a new bed. So, those are 2 pretty big changes looming on his horizon and it's probably just making him anxious. I think if we can use GW to make him feel calm and secure in his room/bed, then that will help. You might also try a homeopathic remedy like Calms Forte -- Hylands makes it for children, and it is supposed to calm a child and allow them to sleep. Perhaps if you can give that to him it will calm his anxiety a bit and help him relax enough to sleep.
Once you get a good night or two in him, then those naps will start taking care of themselves. I think right now he is just so OT. I want you to use GW with naps too. That means twice a day for 3 days you are going to sit next to his bed until he falls asleep. But I want you to sit quietly there, and not interact. Lights should be out. Tell your son ahead of time that you will sit there, but that you need to rest too so you won't be talking to him.
I have a touchy kid, so I know how wound up they can get over change! Let's just give him a few calm days where he has you, and maybe a little naturpathic help to boost your success.