amp/preamp project

right i have got to build a electronics project for college the limmitations are 15v supply voltage and 50watts max current, i want to build something for guitar either a amp or pedel or preamp so got a few questions because i dont know too much about this yet:
1) what does a preamp do and what is the general output value
2) what sort of current and voltage is generated by pickups and fed into a amp?
3) how much voltage and current is ment to be put into the input of a combo amp? and could i preamp my guitar then plug it into my amp?
4)would doing that make the output of my amp louder?
5)does anyone have any schematics of a amp more powerful than 20watts and runs off a 15v power supply or less?
any other ideas would be appreciated, i dont really want to try anything with tubes and valves because i know nothing aout them
thanks