Range to the motion sensors is going to be the most important aspect if I'm going to go this route. Do you think 50 yards is out of the question?
Yes, 50 yards is out of the question. Even with the antenna mods for the "USB interface" (which one??? I assume you are refering to the CM15A, because there is no antenna mod for the CM19A and trying to use the CM19 would create quit a Rube Goldberg operation anyway) you
will be lucky to get even 100 feet RF transmission range in a clearing, considerably less if in the woods. I hope you were not asking about motion detection range because the Eagle Eye under ideal condaitions is only about 20 feet.
The X10 software for the CM15A is "Active Home Pro" and unfortunately you can not use your own graphics in AHP. There are automation programs which will interface to the CM15A and will accept user graphics via an add-on program (Homeseer in one, but is fairly expensive).
BTW: one thing Brian forgot to mention: You can run a CM15A and a UM506 (which would give you a relay closure for the 12V lighting) from an inverter but it must be a "true sine wave" inverter, not a "modified sine wave" inverter. And those babies aren't cheap either.
Another BTW: X10 motion sensors are not likely to detect small animals, 'course if you want to detect big animals (bears, moose, deer, poachers
, etc) they will do that.
Personally, I don't think you can get there from here, on the road you want to travel.