Hi Matt
1) Maybe a couple of meters is good for length just so you can test speed etc without running off the end. 2) The ideal location will be at the front of the layout or better still first track of a staging yard that is easy to get at Make it so the loco can run off it onto the layout should you want to make a longer running test. 3) Yes it should be completly isolated but use a 2 pole double throw center off switch so you can switch the programming track back over to the layout once you have programmed the loco. The reason it needs to be isolated is so you can program a loco (I use the Digitrax PR1 programer with an old Pentium 100 PC) while there are trains running on the layout. 4) The actual purpose is so you can program a loco separate from the rest of the layout. Or have trains running (maybe other people are running you layout) while you are programing a locos CV's on the programing track. I very rarely use my hand held throttle for programing since I use computer connected to the programing track. 5) Specila wiring is as I have mention with a 2 pole double throw centre off switch. This switch has 6 solder terminals. The two middle terms go to the programing track. One side goes to the programer and the other side goes to the layout main feed.Nigel