On the subject of getting more out of your macro lens I would (personally) say no to extension tubes for a 100mm macro lens. They will give you some boost to magnifcation but not a whole lot.
If you were to go for tubes get the Kenko AF tubes, which do come with the electrical contacts which let you control the aperture blades - otherwise you are stuck shooting wide open and that means a razor thin depth of field to work with. You can trick the blades to be shut all the time, but that will mean focusing with very little light which is just as hard to work with. So stump up the extra cash for the kenko tubes if you go that rout.
Personally I would say go for something like a Kenko 1.4 teleconverter (I belive this is compatable with the 100mm macro lens from canon); I use a 1.4 teleconverter all the time with my macro lenses and I find it gives a nice magnification boost; whilst hardly degrading image quality and letting one keep infinty focus.
You can also try out the Raynox series of macro lens diopters - the DCR250 is an affordable and highquality macro diopter (sometimes misslabled a filter) and combined with a 1.4TC (or used alone) gives you again more magnification.
On the subject of focusing rails, you do need these if you are going to shoot from a tripod. Personal experience has also taught me that the
ebay macro focusing rails are one of the better designs (better than the manfrotto!) and are an affordable option (the other is novoflex which is very expensive).
Onto lighting - personally I would say avoid a ringflash as your first flash and instead aim for a proper speedlite flash. A 430EX2 or some sunpak options (there are numerous 3rdparty cheaper options but I honestly don't know them well enough to advise which to go for) would give you a flash with far more versatility than just macro and portrait work (which ringflashes are pretty much limited to). A flashgun combined with a softbox (I used a lumiquest softbox myself) and an offcamera flash cord (or offcamera radio remote) will give you a versatile and good lighting source.
However for lighting advice I honestly would open a new thread for that since there are many options that I simply don't know enough about to comment on