Is there an advantage to having larger molecules for enzyme
inhibitors? (ie. the larger size for finasteride to inhibit
steriod-5alpha-reductase vs. the smaller size of gabaculin as an
inhibitor of _-aminobutyric acid transaminase)

Generally no.  For therapeutic purposes, smaller inhibitors are more
likely to be soluble (and theefore deliverable), and less likely to be
antigenic.