Ademco Vista 20P or Vista 50P system?

[4Technology <jamesclear@xxxxxxxxx>]

We are looking to install a security system on our house. Our initial
research reduded the possible systems to an Ademco 20p or an Ademco
50p. Given we have no experience with these systems personally, we are
seeking advice from the professionals on this board. :-)

We would like...
  - 20 wired zones for doors and windows
  - 4-6 zones for motion detection
  - 4 keypads (one wireless/portable that can be carried within the
house, if possible)
  - 12 wireless zones for external building doors and windows
  - 4 smoke/fire detectors
  - 3 sirens (three unique locations on the house)
  - internet connectivity
  - x10 light/device control capability
  - room for future wired and wireless expansion (for room addition)

There are clearly other factors to consider; however, we are no pros
and could have overlooked the critical point. :-(   Your advice and
guidance is greatly appreciated.

Thanks to all!