okay, i can't answer to all the questions, but here are those i know :
1) it depends on the size of text you want to store, use either text, or bigtext.
2) the ENTER in a textarea is a newline, which can be converted to <br> using nl2br()
3) i don't understand the question, sorry
4) i don't think php can know if the text is highlighted or not.
maybe in javascript.