Arduino hardware programming and setup Nano and Mega

Small company, Have 10 props in 3 rooms that most have a nano bard installed along with a PC connect board. 5 boards currently work, 5 do not. The boards typically have very simple function; to sense the state of a switch (magnetic reed or prox) in the Normally Open (NO) state. when state changes, interrupt the power on a separate line (12v for a magnetic lock, or play a sound from the onboard mp3 file). Wait for the specified amount of time and reset the board. --- There are a few other specific differences between props, but essentially all very simple. We also just bought an Arduino Mega 2560 and a LilyPad MP3 board that can be used. **We do not have access to source code or any original libraries** You would need to download and setup libraries and write all code to be stored at business site. You (programmer) may keep a copy of all code you write. It is your code, and the final working version is ours. We have an install tech onsite to run wires and make connections, but you would need to specifically identify what pins need connected to what item on the Mega 2560 and lilypad. The (5) individual props with their boards would be setup individually. A typical prop would have 1 (or 3 reed switched that need to coincide, or prox ) that when triggered, cause the prop to make a sound from the onboard SDcard and onboard speaker.... or, the trigger would cause an interrupt of a 12v magnetic lock power line causing the lock to open. Once triggered, reset the board after 3 minutes. If you determine it to be more advantageous to use the Mega2560, that would be fine, we can discuss those options. A more detailed list of each prop, and its wire connections and expected function can be provided along with pics. What is expected is that you know C programming skills, libraries, Arduino hardware and ability to work independently and on telephone conference calls. We can also setup remote software (team viewer) and connect individual props to allow programming, compiling and execution to verify working code and prop functionality. Success is determined by working props. We welcome your expertise and questions. Budget flexible.