Flash and RAM Usage

Somewhere I recall seeing a table (or similar) of the amount of free flash and RAM available for JS on the various devices, and how many JS variables it would support, but I can't find it now. Can anyone point me to it?

Also a few related questions:

1. JS typically executes in RAM, so I assume the full size of the JS text is subtracted from available RAM before the rest is allocated to variables?
   
2. What determines whether a JS variable uses 12 or 16 bytes?
   
3. What options are there for "maximizing" flash or RAM space? I believe it's possible to execute code from flash, but with a possible performance penalty. Where can I find more information on that?