I am totally new to computer scrapbooking and have a few questions that hopefully someone can answer. Sorry if these are totally stupid!

First- When you scan in your pics to use, what size picture is best to scan (8x10, 5x7, etc..)? What size is generally used in computer scrapbooking.

Second- If I scan in a wallet size pic, can I set the scanner settings to make it an 8x10 size?
The reason for this question is because I am interested in using a certain picture as the background on a LO and it is a wallet size pic. To use a pic as my background- do I need to scan in an 8x10 for this to work? I know you can streach the photo using the deformation tool (I use PSP), but I don't want it to look distorted.

Third- When I have scanned in a pic, what file type should I save it in? Do I save the LO in the same file type when I am finished?

Anyway, thanks for any help!!