So I'll preface this by saying that this is based on my gestalt of applicants I've reviewed at my school, which is very mission-oriented and highly values service, so there may be some candidate self-selection here skewing averages upward.
So in my mind, I kind of lump all clinical (paid/unpaid/shadowing) and volunteering (clinical and nonclinical) together.
For both categories, I think 500+ hours is very good. 50 hrs of shadowing is plenty in the clinical bucket. In the volunteering bucket, I'd like to see the bulk of it directly with underserved populations and at least 100 hrs nonclinical. Bonus points for leadership and/or advocacy related to the population you serve. I think 100-200 hrs of clinical and of volunteering is the minimum I would find adequate in the context of an otherwise strong application.
Research is not necessary at some schools and is a tacit requirement at others. Mine is one of the ones where it's not necessary so I can't really say how much is "enough".
Not uncommon to see applicants with 1000+ (rarely, 3000+) hours of service or clinical experience. Those applicants are exceptional and very likely to be interviewed if LORs and essays suggest they are a nice, normal person and GPA/MCAT are adequate. But I think 500+ hrs puts you in a position where it's not low enough to get you rejected based on that alone.