I agree with @Covertgrower
It’s use - Use is multi purpose and wide spread for behavioral, emotional, physical ailments as well as recreation.
It’s acquisition - Region dependent - medical marijuana is available as is recreational in some regions.
Quantities to use - strain and tolerance specific (there is a great deal of information on the internet related to specific strains.
How much oil - as the previous answer outlined, strain and growth specific. Some strains are bred for the production of oils/concentrates.
Apologies for the non-specific answers but your questions are quite all encompassing. Personal experimentation, given the relative absence of harmful side effects, is the best approach.
Best of luck and here’s to your good health.