Sorry to hear you're having probs. For relays, you have to make sure that the control side gets full power and ground when the horn button is pressed. If not, you have not have the magnetism to pull the contacts closed. You can supply the control side and check resistance in the load side. Maybe try giving the control side power and ground, if it still doesn't work, it's in the other half of the circuit. Since you know the horn itself works, you can check the wires on the load side for voltage drops (while energized).
For the starter; have someone turn the key while you check for 12v at the soleniod. If it's there, and your starter is grounded properly, it the starter/solenoid. If no power at the solenoid, trace power from the ign. switch. ie. power in, (turn key)---> power out to starter. If you want, you can try powering the small power wire going to the starter at which time the motor should turn.