Kageso's given by the tempest, hom, and competency trials are pretty sucky, so your best bet is to synthesize or refine your gold or orange kagesos.

8th cycle means you have pretty good wielders like yukiri, etc, so I think it is worth spending opals to get kagesos instead of hoarding to get wielders. U can also check for kagesos in "exchange" located at the lower right of the kageso overview tab, it refreshes after some time and offers exclusive wielder kagesos.

As for soul shards, idk tbh, I just do competency trials everyday and recently bought 50 soul shards from Hakuya's item shop. Buying the gold exclusive kagesos of corruno etc. are better options, but being an f2p I only had 4 violet pouches and ended up spending it on soul shards and cores. The event ends tomorrow btw, so better spend it if you haven't.