I am assuming that you are talking about the Pix Universal and the Pix LE. They both will work on the P32 /52 and I think the P31. The LE does not have all the bells and whisles as the Pix U board. You have a lot more options on the Pix Universal. But the LE is cheaper. It all depends on what you want to do with the cam set up. Both are good boards.
The Pix Universal is also a little bigger then the LE.
Welcome to the forum if you need help just post and some one will answer.
I would do a search on P32 cams. (Should be the same for a P31) and look at the various post. Next I would look at the various members webshot pages, My pictures, or other links under the members names and look at their cam set ups. See what cameras fit in what cases. Look at the various set ups to see what you would like it have in your unit. Take their ideas and use them for your unit.
Pixcontroller has a kit that would give you an idea of what you would need to build a cam and the price.
I would have to say the P31 and P32 are totally different. The P32 and P41 are similar, hacks are almost identical. The P31 is a totally different hack, alot harder, with very small solder points. Proceed only if you are confident in your soldering skills.
The Sony U and LE chip can only be used in their respective boards.