There's two ways to approach the budget question -
Approach one: Find out how much money the school is willing/able to give the production, and work with that.
Second - try to figure out what your money needs will be and make a proposal to the school saying you think you'll need x amount of money, and be prepared to give them the list of what you think you'll be spending on it.
Be prepared to have no budget - a school show for 150 audience would typically have no budget, and would be put together with whatever you can beg or borrow.
You technical questions are all about sound, and sound equipment. FOH = front of house, an english abbreviation. FOH technician is the person running the sound board. FOH is a generic abbreviation that folks will use to mean anything relating to the lobby, a sound/light booth that's at the back of a house, sometimes the box office, etc.
Most small band riders have specifications for what kind of sound equipment that they will need, as most road houses don't have much, if any, house equipment. What you need to do is contact each band that is playing and make sure that they each have the equipment that they need to perform (which they probably do, since they are small bands), but you should also find out what sound equipment is available at your venue and make sure that that it will work with what your bands will need.
-Centaura