HELP. with matting and framing.

What is a good basic proportion to use for matting? I just had one cut, supplying the size of frame and photo. The opening is almost too big and it is really hard to attach photo to it. How much overlap should there be??? And how does one attach photo. ? Do I attach it to cutout mat or attach it to a cardboard and hope it is in the correct place.

Along these lines what is best way to choose mat color???

And even the frame color and size??

WHEW. Thanks for any opinions and help with this. In the past I have bought ready cut out mats but want to be more selective and creative.
Cinderella

A healthy border is recommended for archival purposes (an inch should do). If anything attacks the paper, it has a way to go to hit the image, then. As for attachment, there's a special tape for this. As for color, that's subjective, but I say black or white is the only appropriate color.