You might need to have the school manage your money. You may be able to have the school or science department order supplies you will need. You should be able to get classrooms for after-school practices. Obviously, intelligence is very important for the knowledge events, but don t ignore dedication, attitude, honesty, ingenuity and character. Engineering events require mechanical aptitude in working with wood, circuits and finely-tuned mechanisms.
Some evens require experimentation for finding a solution.
This is the really hard thing to do. If you are lucky, you can pick more students than you need and start getting a better idea of which students will make the best team members. You will also have to decide which students to assign to which events. You should consider a policy that allows for competition for spots on events, but one which gives the head coach the final decision. The students competing in an event must know the rules better than the head coach.