If I move a character from my hidden area to my visible area via an effect can I place them in any open spot as long as it doesn't specify? If charcter A is being attacked, can I move character B from my hidden area next to character A to reinforce??

As long as the effect moving the hidden character allows you to move it to the visible area and it does not specify where to put it you can put it into any open space.
The effect must specify that you can move a hidden character to the visible area. If it say something like "move target hidden character" you can only move in the hidden area.

Yeah I thought that was how it worked. There was a question in a game the other night, I had an effect that said that I may move a hidden character to my visible area and a visible character to my hidden area, so I picked them both up and switched their positions. I can't remember what the card was, but it wasn't an "if you do then move a character from your visible area to your hidden" as I was able to pick them both up at the same time.

Anyways, the idea came up that if you move a character from your hidden to your visible area that it must not be adjacent to any other character. I wanted to make sure that this was not the case.