First of all, I'd be buying/building opposite a park, in a street that is not super tiny, but is also not a main road. Bus access would also be a bonus.
Dedicated nook/cupboard off the garage for the control center, with under-slab ducts out to the yard.
All "Xmas Lights" power / outside power points all wired to a central isolator switch / circuit.
Outside power outlets & Data runs to garden(s)
I'd build a gate-house style structure at the letterbox. Something else to put lights on, as well being perfect vantage point for CCTV
I'd also landscape in some sort of 'guard tower' gazebo[/size] design - perhaps, up hill or towards the back of the display. Naturally covered in lights too - but you can sit back/hide inside it whilst the show is running during non busy times.
For under drive conduits either use 2 x 32mm conduits or if you really want to plan ahead drop in a 100mm water pipe
I'd definitely go the 100mm pipe idea, with pits at either end so your pipe doesn't flood. Bigger pipe means you can easily drag more cables through later.