there were a couple of models of the RCP40. the early ones would have a fixed speed, meaning they ran EP2 and unless it's been modified it won't be much use now. The later models, had variable speeds and temps, so you could run a few different processes. I don't think any of them have been made in the past ten years or so. The models that replaced them were the ACP processors--both the RCP and the ACP were made by Thermophot for Durst, so you might be able to get some help from them. I have an RCP 20, and have only minor experience with the RCP40. They can be good or bad--depending on the age and condition--but the parts aren't available for them anymore and there's no tech support.
as for RA4 in a processor, you will use several liters or more of chemistry and it won't be one-shot. You'll have to monitor it somehow--control strips are the way labs do it--and you'll have to replenish the solutions to keep the activity up, keep the pH in check, and possibly check the specific gravity. The dev will be carried directly over in the blix--which will cause some problems if you don't repl. properly. Some of the older EP2 type machines that had 3 tanks can be good for RA4 because you can use a stop. The basic RCP40 would have been for processing only, with the wash and dryer as an add-on unit. If you don't have the whole thing, then you'll need to wash outside the machine and use some sort of dryer as well. When you color print, the prints need to be dry before you do any corrections.
If you print everyday though, the processor makes sense and you can make it work. But if you just sporadically print--you'll waste money on the chemistry, you won't have enough throughput to keep the replenishment working right, and you'll have to use higher rates of replenisher as well. You'll also spend a little bit of time doing chemical mixing and maintenance. If you have to drain the machine frequently--it will get old fast. You can probably get a couple of weeks out properly maintained chemistry in a small machine though....when you dump it & start over, you'll need to pull the racks out and clean them etc. This will take maybe a half hour or so. So--it saves time, but you also need to use it to make it work.