SKip, good choice on the CP31. I have 2 of those, they are great machines. RA-RT keeps fine even in the orignal bottles, for years, in my experience.

C-41 keeping: Developer is the only one of real concern here. I have the "makes 5 Gallons" developer from Pakor.com (about $26). I make 5L at a time, after figuring out the proportions. Part C (CD-3 or CD-4 ? ) is the one most prone to oxidation. I refill the concentrate bottles with inert gas and seal them with a layer of saran wrap between cap and bottle after mixing up a 5L batch. It's kept fine so far through 2 batches, about a year or so, using the above method. I need to mix a new batch soon so will have a look at it. If the Part C is discolored/dark at all, that's a good indication it's bad, from my recollection.

Once mixed, I try to use up the C-41 batch in a week or two if possible. The longest I think I kept a mixed batch of C41 developer without it going bad was about 6 or 8 weeks, but that was a stretch and it was pretty oxidized and not working great by the end. I save up my shot film now and run the whole 5L at once within a week or so, if possible. (5L = 48 rolls of 120 or 35mm, via a SuperSidekick4. )

-Ed