[NotDeadYet]

Sorry to hear about your diagnosis.

Anyway, on to your questions...

The way SCRs work, the ppO2 of the gas you are breathing is normally lower than what the ppO2 of the gas driving the RB would be were you breathing it on normal OC equipment. While EAN48 at 20m would indeed give you 1.44bar if you were breathing it through a regulator, in the loop of a SCR it would be lower. It all depends on flow rates and breathing rate but would be in the region of 1.4 or less.

I've used Ray components in my homebuilt rebreathers, like most Draeger parts they are very well made. I've got a Ray scrubber sitting in my garage ready to become my bail out rebreather when I can be bothered. I've used a complete Ray once, can't say it was an especially bad feeling but it wasn't great either.

As someone says above, why not just dive on nitrox on OC kit? Rebreathers, even simple ones, require a lot more preparation and post dive TLC than OC kit does. You have to be fairly certain that your MS is going to leave you in a position to do this. On the other hand I can appreciate you are also looking for something to keep up your interest if your diving is being limited. Bear in mind not cleaning your regs properly for a few dives is unlikely to do you any harm, this is not the case with a rebreather. Similarly, you can't afford to cut any corners in your prep as you can with a normal set up. You pretty much need to get it right each time.

RB diving is brilliant and definitely the way forward! I'd suggest paying a little more and look at the Dolphin. There were a couple on e-bay the other day.