1. Any recommendations for specific printers? If not, is there something I should look for to help know if it will work properly on Linux?
2. How do you design your own 3D objects for printing? Is there open source software you would recommend?
3. Where do you find existing things to print? Are there online repositories? Is there a standard for printer files or are files unique/proprietary to individual printers?
First, I use a Prusa MK4 printer. They're great. I use PrusaSlicer to convert the model files into the gcode files the printer wants. It has a linux version and is quite capable.
3D printers are standalone machines that don't require integration into your OS. At its clunkiest, you just copy the sliced models to the printer and away it goes, but there are things that make the experience more seamless (such as running an Octoprint server, and many printers, including the MK4, can provide their own web interface).
I design my own models about 90% of the time. I use FreeCAD and OpenSCAD for almost all my modelling. They can both generate the stl files your slicer will need. Both of these have a pretty steep learning curve, but once you've learned them they're great.
When I'm looking for existing models to print, I usually find what I need at one of two repositories: printables.com and thingiverse.com. General web searching is sometimes fruitful as well.
In short, don't sweat the Linux aspect of this. It matters far less in the 3D printing world than you probably expect.
1) Bambu Labs X1 Carbon (X1C)
The X1C was my first printer, and now I have two. My research led me to the Bambu X1C as it was the most automated plug and play printer without much hassle. With it's design I could also print with alot more types of filaments. I've been very happy my printer, I got a 2nd a few months later. I have over 400 hours on each printer without any issues. I've printed many 3d parts for the printer to make it last longer and provide a better experience.
You will need a slicer program to go from 3d model to 3d printer. I recommend the Orca Slicer.
https://github.com/SoftFever/OrcaSlicer
2) 3d Design is through 3D Software. Fusion 360(free depending on license), FreeCAD, OpenSCAD
3) Many sites to download models and print. Reach comments as the author may give tips for printing.
https://www.printables.com/
https://www.thingiverse.com/
https://makerworld.com/en/models/categories
4) FilamentsI'd buy a ton of PLA, and test. Then start buying the type you need for the project.
Good luck!
2. I use blender if I want to make something artistic looking (works fine on linux), and onshape if I want to make something technical (web based, works on anything)
3. thangs.com is a good aggregation site for models that pulls from places like thingiverse and printables. Printer files are usually STL or STEP for the models themselves, then you use a slicer such as cura to convert it into a printer-specific file, which is .gcode file usually, which contains printer movement commands. I've not seen any proprietary files for specific printer, but I may just have missed them
3d printing is very open. I use nothing proprietary .
Most any printer should be fine with linux, I think. I'm using Repetier-Host to feed my printer via USB, you could use octoprint from any linux system or dedicate a raspi to it to do the same.
I use OpenSCAD to design things, and publish models on printables: https://www.printables.com/@h2odragon_1916718/models
2. You can definitely use Blender, just make sure you're using the proper dimensions (e.g. millimeters), you can then export your model as STL, and then use Cura or any other slicer you may like to get a gcode file which you can then send to your printer or load into a microSD card that you can select from the printer menu. Quick tip: if you just want to do a quick test, make sure to select the draft profile on your slicer, this way the generated gcode file won't take as long to print, the quality may be rough, but you can make sure that what you want to print will be printed successfully without having to wait twice or three times as long. Quick Blender starter: using the default cube shown on start, it measures 20mm per side, just go into edit mode, remove the top face, then select all the faces, use solidify tool, enter a thickness of at least 2mm, leave edit mode, export STL, slice in Cura, and you should have quick little test box to print. Scale appropriately for a different size, and use your design skills to make round corners in order to avoid sharp edges.
3. Thingiverse has plenty to choose from, look out for the dimensions of the objects, and for any material recommendations or printing notes.