1. Most people use roadbed for several reasons. It helps deaden the sound from the engines and it provides a profile for the ballast. Besides, you glue it down and it becomes the guide line for the track. It is also easier to drive the track nails into the cork or other soft roadbed as opposed to plywood.
2. Old track? Any track can be cleaned with alcohol, silver polish cream or the special track erasers made just for this purpose. Do not use any sandpaper as this will leave scratches that will attract dirt faster. Very fine steel wool can be used, but not the coarse type. If you are reusing track that was glued down, soak it in warm water to remove the glue.
3. I solder all mine except at insulated joiner of course. With DCC, this provides a better electrical connection. There are enough insulated joiners in my layout to provide for expansion and contraction of the rails due to temperature variations.
4. I solder them as I lay the track. Especially at the curved joints. This assures a smooth curve while laying the track. Other than this application, which I recommend, soldering of the joints is up to you.
5. 40 watts is perfect. Don't forget to use "heat sinks" on either side of the joint before you solder.
6. I tried one of those and was disappointed. It does not get hot enough to solder my HO scale track. Other people like it. I'll stick to the hot tip.
B-)
