Congratulations on the new printer!
When I started out, I was on a desert island. For learning the ropes, I found
Thangs, a search engine for models, was huge in helping me find parts for smaller rockets and tools. Later, I would take those .STL files and modify them in
TinkerCAD. It's a good place to start with lots of tutorials. I then pushed myself to start learning
OnShape and SCAD, though admittedly, I'm better with OnShape. I think working with any CAD app will enhance your experience but with so many models available, there's no urgency to become a CAD master. Take your time and enjoy the journey. For OnShape, like Fusion360, your designs are public so don't put anything out there you're not willing to share (or pay for a subscription). YouTube is a good resource for all the things. You just have to weed through the noise of irrelevant content (like anything else Internet-related)
I, too, use Amazon for my filaments. Having no educational resources other than those mentioned above, I started with PLA and then moved up to PLA+. Duramic is the brand that seems to work best for me but don't limit yourself. Just be careful of the off-gassing, as
@Huxter mentioned. Personally, I'm working up to the Nylon with Carbon Fiber. PLA+ has been great for most of my projects, but I'm now in the area where plywood would be better but I don't have the tools or money to build my own fins or Centering Rings yet. Maybe Santa will bring me a Laser Cutter or a Bambu!
For the PC, you probably only
NEED it for grabbing models and transferring them to the printer. I added an OrangePi computer to mine and I'm running OctoPrint, so I can fire up its web app and transfer gcode directly to it and control it remotely. I understand that the Bambu printers have something similar built in so that might be needed. I guarantee that your experience and toolset will grow organically, proportionally to the amount you use it.
Also, feel free to ask more questions here. There are lots of great people who are printing and are willing to help. Just be patient and don't rush it b/c it can be frustrating when a 10hr print falls over and "spaghetties" all over your print bed. That's just part of the journey.
Best of luck to you and welcome to the clubhouse.