I'm as new to 3d as you are, but I have a LOT of experience in the digital print world. I can tell you what I am doing and what I think is important to me. what works for you is up to you. The links are what I've bought and in no way an endorsement of the products.
Start with the basics. Buy a good magnifying glass and look at the printed piece and look at the g-code. Choose the kind and brand of filament you want to use, then using the magnifying glass, tune your printer. Find some simple test files and print them repeatedly, changing one variable at a time.
I went with hatchbox pla as my filament, mostly because of amazon prime and reviews.
https://www.amazon.com/gp/product/B00J0 ... UTF8&psc=1
Get a glue stick to use under prints.
I purchased tools to be able to change the nozzle and a selection of
(NOT MK8) nozzles (A10T) to test. I want bigger prints, so I'm heading towards a larger nozzle and lower quality prints. You can also go the other way, of finer nozzles and more detailed prints. 3d is always a balance of quality versus speed. By tuning the filament to be the best it can be, a courser nozzle can give good results and a fine nozzle look bad. The .4mm is a nice middle ground.
https://www.amazon.com/gp/product/B0793 ... UTF8&psc=1
I hate the SD card, so I'm working on setting up an octoprint server, so I can control a printer across the room and with a little internet savvy, around the world. By using an old laptop, I believe I can replace using the SD card for free.
https://community.octoprint.org/t/setti ... stallation
I've ordered and installed a glass bed
https://www.ebay.com/itm/235x235mm-Boro ... 2749.l2649
I've bought a filament pen, so I can use the same PLA as the 3d printer and fix any problems. I'm now looking for thermal sculpting tools that I can smooth the added filament, because sanding doesn't work well.
https://www.ebay.com/itm/3D-Printing-Ar ... 2749.l2649
I've bought and am testing a water soluble filament, that I can print internal structure and simply soak the print to make it go away. Tuning for soluble filament is a bit different than PLA and needs tuning for the 2 to play well together.
I have chosen to spend money to make my life easier. I purchased simplify 3d, because it is simple an works. Free options exist, but I have SO MUCH TO LEARN, that for$150, i just could make all slicing issues go away. Should I have learned cura? (maybe?) For upgrades, think about what will make your life easier or produce a more desired output.
Most important, have fun! It is far too easy to get overwhelmed.