[jordinho]

First of all please note that i am not an electrician or any braniac in electronics. I was just so eager to make it happen that i took some chances with the retrofit. Cutting wires, dismantling the door panel and all these things are tricky but with patience and the know how you can make it too.
Feel free to ask as many questions you need and post the pictures with the end result.

Spare wire - Ordinary wire(speakers wires are just fine). It will be helpful that the wires are doubled because you need to connect 2 wired to two different locations.
Junction box - It is not truly required. You can just connect the ends together and tape them. the junction box i used made the connection more tight and shock proof. It is an ordinary electrical connection. It is used for splitting the wires. You need it to "transform" one main wire into 3 other ones that will finally lead to the LEDs.
Wires-You are correct. You require these two wires to power up your LEDs. So, you need to cut one of them(let's say window motor) this resulting into freshly cut ends. To these 2 ends you attach one of your wires and tape all these 3 ends together (2 from your window motor and the extra one - your wire). The same procedure you'll follow with the other live wire you need (window button). TEST 5 times before you cut. For example what i did was to test the LED's in the connector pins/slots and when i was sure what wires are good for me that's when i used the scissor. The wires i used were much thicker. Maybe that is why it looks that both my wires are attached to each wire from the car system.
Parts order - In Romania there are several websites that are selling OEM BMW parts, cheaper than the dealers. I can't really help you with this matter. The website i used is this one bavauto.ro
I don't know where is part 2 from live4today. I also waited for it for a long time until i gave up and took the matters into my own hands.
Car side connector or door side connector - Each door has a lot of things that need to be powered up. This means that there are a lot of wires needed. They cannot run all the way to the main power system. These wires have connection boxes or connectors or i am not sure what is the correct name in some conspicuous places i order to disconnect them in need. Let's say you need to remove the door - you need to disconnect the wires somehow. Therefore there's a connection box on the side of each door - where the hinges are - inside the rubber cover.

I dont have anymore photos. I was so into this job that i forgot to take pictures of some steps. Sorry.

But i can help with answers to other questions, Take care.