Hi, thanks for your questions.  To answer them:

1. The lightbars will be 90% assembled.  You'll still need to move the small 1x1 transparent blue slopes from your existing Ecto and transfer them to the lightbar you'll receive with our kit.  Also the two center gray slopes with the black lines will need to be re-attached.  That should be about it.
2. The motor fits inside the Ecto-1, directly under where the axle goes up to the roof.  You can see a photo of it here-- scroll down to the section that says "A Motor for the Roof Gear."  There you'll see a square red motor positioned next to the seat.  That's the motor.  It connects to the main controller board for our kit, and is powered by the same power source as the rest of the kit.
3. In terms of power, the kit ships with a USB cable, so you can use any iPhone or iPad-type wall charger to power the kit, or a USB battery bank.  You have the option to purchase a LiPo power source when purchasing the kit (click here for that pre-order page, and you'll see two options under "Kit Configuration").  You'll need to order the LiPo battery and charger separately-- we have links on the preorder page to the recommended battery and charger so you can order those.  With the LiPo option, you can have the battery inside the rear of the Ecto-1, so it can be self-contained.  There is a master power switch on the remote control for turning it on and off.
4. For the BrickScreens, yes, possibly, though our smallest screen is still larger than the printed tiles on any of the back panels.  There is one connecting plug on the main controller where something like the screen can be connected.  We're actually working to see if we can make an oscilloscope for the back, like in the film, and if we can make this, it will have our smallest screen yet.  No date on that, however, and no guarantee we'll be able to make it, and no price yet.  Stay tuned-- if we do offer this, it will be available as an add-on.

I hope this information helps-- please let us know if you have any further questions.  Thank you again for your interest in this kit!

Chris Carr Wonderful!  Thank you very much.  Shipping from the USA.