A couple issues regarding the Cloud City processing vane. You say, "As for the vane it is a bit of a design flaw. I think that Luke was supposed to have reached there through the long tunnel but they put the support pole in the wrong position on the matte which caused confusion."
I knew I'd seen a cutaway in a book somewhere, so I did some looking around and found this:
You can see that the long tunnel is actually a tram-tunnel probably intended to carry cargo back and forth from the city to the processing plant in the vane. The carbonite chamber is at the very top, and it seems to me that the lighted tube Luke walks through is all within the upper part of that vane, and not in the support arm. That should save you some trouble repainting the matte.
Also, when Luke exits the tunnel, a large gate closes behind him, but when we see the same tunnel entrance from a different angle a few seconds later, the gate is open.
Just to play devil's advocate here, but are these cutaway books really canon or are they skirting the line towards EU? The reason I say this is because in Empire, when the Imperial Officer drags Leia through the door and Luke follows into the darkness, he goes through the door from the main white hallways of Cloud City proper and is suddenly funneled up an elevator into the freeze chamber. I don't see anything in this cutaway that would provide walking access back to Cloud City hallways and I just don't think Leia's captors would lead their prisoners into a dead end, which they clearly don't because a few minutes later they are back in the white hallways. The whole thing doesn't make sense, I guess.