tuning is kinda one of those things that as you learn more about, you realize you ask more questions than finding answers. Like you said difference between springs and oil - quick answer is springs are paired to the cars weight to absorb landings at an even rate (the back and front move up and down at an equal rate) and oil changes how fast (or slow) that change happens.
The shock tower and arm holes affect the shock angle, which translates to how fast they go up and down. A more up-down angle, its fast. More angled, its slower. IDK if this is equal to a slightly stiffer spring or heavier shock oil. I think its fine-tuning spring rates.
Shock oil i think affects how far up and down the shock will go in an set period of time. example - when the car drops, the suspension takes about .5 second to react up and down (ASSUMPTION NOT FACT). A light oil and the shock will use a lot more tavel in that .5 second. A heavier oil slows down reaction time, so in that same .5 second landing means the shock has less time to travel up and down.
My head is already spinning thinking about this so much without applying it to corning speed and all that regular tuning stuff. The best thing is to get consistent enough to be able to feel what one change does. You only really wanna do one, maybe two changes at a time. Drive it around and see if you are faster or slower and asking yourself where am I losing speed, where is it hard to control, etc. A pro setup is usually something to just get you going in the right direction. From there you decide what you need more or less of. There's lots of free guides on youtube, but you really wanna hear from an racer with some engineering know-how. They really understand whats going on and why. Even with good explanations its still kinda hard to know without getting out there and experiencing the changes first hand. Those practice tuning days make me wish I had a mechanic to make the changes for me and I just race and give feedback.
Tuning is something that also changes as your skills grow. You can tune-in "traning wheels" that make the car easier to drive by slowing the reaction speed, getting it to center easier, less grip, etc. As you get better the car can be more nimble and you change some simple things, like toe-in and camber, and the car will react faster, or you feel more reactions from the car.