Bjn, that description just hits it perfectly. One thing not mentioned is that each of those parts (except the batteries and lens) is not that easy to get. You can't just order them whenever you feel like it, you have to wait for the next group buy or batch to be made, or wait til your missing shows up on B/S/T and pounce on it before someone else does. Also, you need at least one battery charger, maybe several if you want to charge all the batteries at the same time.
I have most of the parts for an Mag85BT with a few more expected to arrive soon (WA bulbs and MC switch core) from the group buys, but I've begun to think it's kind of a questionable project. An MC60 is almost as bright, much more practical to use (drop-in charger), is much easier to acquire (buy a stock Magcharger and put in a 1160 bulb), and ends up costing about the same. If you get the 3-to-D's and 1185 bulb, you can upgrade it to an MC85 and still use the stock charger by removing one resistor.