website page sizes... can you explain the different sizes available.

do they show up different on different devices?
do they resize automatically on different browsers?
how big can a custom web page be?
how long can a page be? or recommended?

i started a pretty big website...now i feel like its to skinny is there a way to resize it? or do i have to tweek each page? (35+ pages)

thank you all for any input!

Frank