Asterisk Dial plan with GUI

I need an asterisk PBX dial plan and gui created that will allow entry of external numbers (cell phones) to be dialed. When an inbound call comes in, entries will be dialed round robin. I need a configurable timeout for how long each number will be given to answer, globally as well as a per number override. Only one outbound call to a given cell phone at any time. If another call comes into the system, avoid sending the call to any cell phone number already on a call. Also, a configurable timeout for the total time the caller waits in this queue of cell phones. I need a configurable option of where to send the call after this timeout. The destination could be voicemail or back into this same group. A message needs to play to the caller after a set number of rings or seconds, to let them know someone will be right with them. If all cell phones are on a call, play a message and play MOH, and repeat message every x number of minutes. The same queue timeout will take effect if all numbers are on a call. I use FreePBX, so this will need to be a custom configuration that does not overwrite or get overwritten by FreePBX.