So, i’m new to scuba diving, but i enjoy it a lot so I plan on buying some gear. And I just had a few small questions.
How accurate does a regulator need to be? How can I make sure that the regulator is
reading correctly, like a short test or something?

Are you talking about regulator or pressure gage? Regulator is a part that connected to a air cylinder. It has 2 type of outputs. 1 HP : to connect pressure gage to see how many bars you have, 2 LP connects to maps, inflator, horn etc. On LP circuit there is approximately 8-10 bars. There is no need to be accurate, because on the maps, which you hold in your mouth, air is regulating again according to the current depth.

I think you should wait and get experience. Because diving is very enjoyable, on the other hand very serious sports. Small mistakes may kill you.