To get to the final battle, do you have to complete the all the shots to each scene or do you just have to start the scene and the points on top of that are just a bonus?

Yeah, I just asked because I got to the final scene the first night I had the game. I didn't understand the rules but I was hitting the scene starter at will. It was a lucky slop game. I bumped the game up to 5 balls and still haven't gotten close to doing that again. When I got to the final scene, at first I had wondered if some factory setting had been changed to make it easy. I don't consider that my best game though. I have had other games that I thought were a lot better skillwise were I was had 4 ramp combos.

I think that you could do this with a simple flip-flop circuit that uses the kick er switch and whatever that activates when it falls out of the playfield. I think you could do this with mechanical relays or electrical nand gates pretty easily.
Getting a mechanical bistable latching relay is probably simplier than using gates and chips. I don't know the voltage the switches operate at or the wattage of your lights but you probably just need something as simple as this.

http://www.willow.co.uk/html/components/com_virtuemart/shop_image/product/Duplicates/pdfs/DG76.pdf

http://www05.abb.com/global/scot/scot229.nsf/veritydisplay/539fc930aaf71461c12577ed002e44e3/$file/RXPSU.pdf

Same here. I maybe overpaid a bit but don't regret the purchase. It is a great game. The more I play other machines the more I realize how well laid out Shadow's playfield is. The sound is great, too but the machine doesn't have any shitty shots.