Nice job. I once designed something for “Old” Crucible: https://www.grimtools.com/calc/pZr33M0N
It might have some useful ideas in terms of defence and easy itemisation.
Protip: It requires 17% CDR to proc 1 seeker/second if you bind it to CoF. So a Chronomancer’s or Supercharged prefix on your shield is key. That also helps you spam more runes too.