Subscription box build-a-box flow (Shopify Plus)

Frost & Flour sells baking-mix subscriptions (4k subscribers, Shopify Plus + Recharge). Churn surveys say people want to pick their mixes. Build a 'build your box' flow: monthly deadline, 3-5 slots, dietary filters, nice animations, works inside our existing customer account area. Recharge API experience strongly preferred. Design mockups exist; you'll make them real.