Hello and thank you for your post and for being a customer!  You asked about any tips to mount the battery box inside Technic vehicles.  In general, no specific tips, though a rubber band or two may help keep the box in place against the frame.  You can also make a bracket for the battery box using extra Technic beams you may have on hand.

For the LEDs, here are some tips for mounting them inside Technic elements.  There are three main ways to mount the LEDs:

1. Using a Technic half-pin and round clear or colored plates on top of the half-pin.  This mounts the LED on top of the Technic element.
2. Placing the LEDs directly under clear or colored plates.
3. Using a round 1x1 plate with hole to mount the LED on the  back of of the Technic element.

For the first method, here's a photo of how that looks (pictured here inside the Volvo loader):

  This method works really well, though you do need to use plates on the top, not tiles (there isn't enough room under the tile for the LED and circuit board).

For the second method, here are some photos (again, using the Volvo loader as an example):

  With this method, the clear or colored plate sticks up a little bit, but this is barely noticeable when looking at the finished model.

For the third method, here are some photos of how that works:

  The top photo shows the LED being mounted behind a round 1x1 orange plate, while the bottom photo shows how to mount the LED behind an orange light cover with pin.  In both photos, the round black plates are the ones with holes (part number 85861).

The little black tube is something we've been testing to keep the light from shining through the sides of the Technic part.  This is helpful when working with lighter-colored Technic beams and bricks, but isn't needed when working with darker beams and bricks.  I'll go ahead and include some of these tubing sections with your order in case you need them.  Longer-term, we're probably going to be selling some mounting kits that include both the tubing sections and the round plates with holes.

I hope this information is helpful for mounting your lights inside Technic elements-- let us know if you have any additional questions.  And make sure to post photos of your final project when complete!

For the LEC, yes it does retain settings even when the power is turned off, so you don't need to access it every time to re-program the settings.

For the wires, they are very flexible, and the Pico LED plugs can be fed through Technic brick/beam holes.  This is a helpful way to hide excess cable-- just wind it around a brick or beam:

You can also use the sticky squares included with your lighting kit to mount adapters directly to parts: 

Hopefully these photos help give some ideas.  You can also find more photos in our Flickr feed here, here, or here.

Regarding the topbar, we're looking at making this an off-the-shelf part.  Stay tuned!

Thank you again for your post, and again, best of luck with your project!

Qamqualler We sent your order out today-- let us know what you think when you receive it!