problems with lilypond

[liang seng]

Hi, I have another problem. When inserting tempo markings such as Allegro, 
Andante, Largo etc, do I use \markup before a note or I use the \header 
\meter="Allegro"? What if I need to insert a tempo marking in the middle of 
a piece? Then surely the latter method will not work.
2. I find that when using both methods, the word is too near the staff below 
it. How do I lenghten the distance between them?
3. This is for a line of music. But suppose I would like to combine several 
staves into a score (eg string quartet), how do I make sure that the tempo 
markings only appear at the uppermost staff and not every staff since each 
individual staff has its own tempo marking.
Thank you very much.
4. How do I make a brace (like the one in the piano staff) in a string 
quartet score? The brace only needs to span two staves. However all the 
staves are connected by a vertical bracket.
Yours sincerely
Seng Liang.