ECP is almost identical to an RA4 paper in the sense that it is balanced for about 50R filtration with a tungsten light for starters. It can be spooled in 35mm cassettes and then exposed using a simple copier attached to your camera. The ASA rating is pretty slow with all of the filtration, so I would start at around ISO 10 or thereabouts.
The slides you get, if done properly, will far exceed any E6 film. This is due to the huge latitude which is impossible with the E6 process.
As for rem jet. We used a sponge to remove it with a Sodium Carbonate solution. The emulsion never touched the solution, just the back. But, I have seen rem jet lodged in emulsion and it is a problem if not done correctly. The particles are very fine and often do not show up until you do an enlargement.