I've set up Octoprint on a Pi 3B for my MK3. It works great, was easy to set up and I can't imagine fiddling with SD cards anymore, and it easily supports a camera. I ran Octoprint on an older Pi model B with the Lulzbot Mini and that worked fine, it did require a network cable or USB Wifi dongle and a camera would have been a heavy load for that old Pi. The Pi's that have Wifi built in make that easier. Octoprint will run on a Pi Zero but they don't recommend it (many people still do it). It works ok as long as you don't put a camera or too many plug-ins. Anything stronger than a Pi Zero will handle Octoprint quite well. The Zero 2 W would be great if we could get them. A Pi4 is not needed for this, but of course it will work, and any memory size model is fine. Compute module 4's are also fine and are a bit more available but require a carrier board to get to the I/O, and wifi is optional, plus there are many memory configurations but any of those will work. Just this weekend there were some CM4's available and they didn't sell out for hours, Pi's usually sell out in 30 minutes or less when they are available. The Pi3's are excellent and can be a bargain in today's market.
On the next level we have a fork in the road. There is the Reprap highway, and the Klipper highway (there are some other routes but less interesting for this discussion). The Duet boards are at the top of the Reprap food chain, and there are cheap clones of those, as well as Reprap firmware ported to other boards. It's a good way to go, and does just about everything one would want to do. It has it's own interface setup for the web and print queueing, etc. Config is text files. It is starting over in terms of getting your printer to print well, and I don't see as much community choosing this route, but it is a solid choice.
The other highway is Klipper which has been really popular lately and has been growing faster. Klipper is a dual processing architecture and popular setups are a Raspberry Pi for the high level motion planning and user interfacing, while the low level timing and controls are done with the printer microcontroller. The microcontroller can be any of a large set of compatible boards from 8 bit to 32 bit. Klipper generates the binary that you load once into the microcontroller, and all the configuration is done in text based config files in the Pi (you don't have to keep re-loading the microcontroller). The Pi does all the trajectory and motion planning computations and feeds the low level instructions to the controller via a serial link. There are three commonly used web interfaces - Mainsail, Fluidd and Octoprint. So you get to choose. Mainsail, Fluidd and Klipper are said to run fine on even a Pi Zero, Octoprint requires more CPU resources due to it's implementation and design so a Pi3 or Zero 2W or better are recommended. Pi4's work fine, even the small memory models.
Octoprint with plug-ins have more options and features than Mainsail and Fluidd. But Mainsail and Fluidd are lighter weight and do most everything, and they are improving. You can use more than one if your Pi has the resources.
Since you have ordered the Rambo from Prusa you have a couple of efficient choices. One is to run Octoprint on a compatible board and connect it to the Rambo with USB. It's probably easiest on a Pi, but it can run on other boards or a PC. That's probably the simplest and wisest path to follow at this juncture. The other option is to run Klipper on a Pi and load the Rambo with the Klipper firmware. This is much more involved and steps away from all the wonderful Prusa support, and it has a much larger learning curve. Doing this on your only printer would be adventurous.
I am building a Duet based printer (Railcore) and a Klipper based printer (Voron Trident) and I'm keeping my Prusa fairly close to stock (at the moment it has a Dragon hotend, but that changes almost nothing else as it's a V6 drop-in), plus it has the Pi with Octoprint. I think it is best to experiment with a second printer and keep one solid reliable primary printer working - I might need a part at any time, never want to be without one working machine. I also keep spare parts on hand so I can fix the Prusa no matter what.
I've spent too much time researching and collecting parts, I need to get those last few more parts and get these projects finished - before another better upgrade comes along...
Happy Printing!
