i'm a relatively new stacker, but my strategy for my stack is more or less:
10oz bars (i really like perth mint here) and 1oz gov mint rolls (ASE mainly) for weight
kooks and lunars for flipping
as a collector, i'm also interested in completing the lunar/kook sets myself, but thats more for me rather than as an investment.
that way i have the best of both worlds. the trick is to determine what is a suitable ratio for you in terms of weight:semi-numi, and that ratio will be dependent upon your stacking goal/time frame.