Brake fluid info

[devils_fuel]

Just wondering a few things, i'll be changing my calipers over this weekend and wondering about fluids. (also to add to the OC database.

1 - how much fluid is in the brake system (average)
2 - roughly how much am i going to loose when changing the calipers (hoses will stay on)
3 - what fluid should i use to top up, standard DOT4 or high performance 5.1?
4 - is there any major difference in fluid?
5 - can the fluids be mixed; if DOT4 is already in the system, can i top up with 5.1, or would the entire system need emptied adn refilling

1. not sure
2. not much if you put the flexies hanging up and a cap on the end - it will stain tarmac etc if in contact
3. i used DOT4
4. not sure
5. never mix as they have different boiling points