Sorry to hear that. As you know moving is pretty stressful on kitties just like it is for humans, but even more so.
To answer your first question on if there is a reason why he is doing this, the answer is simple, "Of course". To understand you need to know how cats think and sense the world. Cats rely on scents and marking their territory with their scents so they and other cats will know what is theirs. So the next time your cat scratches your prized couch, he is not doing this to reck it. He is only saying "hey, I was here and this is mine". Cats have sense glands on the pads of their paws, as well as their face, and tip of their tail. The move disrupted your cat and this is his way to remark his new territory.
As for your other questions, I would say yes, only because I don't think a cat can have too many appropriate scratching areas. However, you don't have to as you say he had a scratching post and I assume he still does (if he doesn't anymore, than yes go out and get him a new one).
However this won't completely solve the problem. Unfortunately, you are going to have to start from close to the beginning again by trying to make the furniture be not fun to scratch and the post a good thing to use instead.
I would also suggest using a cat phenome to help calm Otis in the new place and make it less likely that he would scratch the furniture. Feliway is one such product that you may have heard about.