Develop custom subscription checkout solution for Shopify using Stripe

I'm looking for an experienced developer for a project of significant scale. We have developed the UI for a shopify site to develop a custom checkout solution using stripe. 1. The site needs to be able accommodate one-off transactions (order a 8 cartridges) as well as subscriptions (recurring order of 8 cartridges per month). 2. We use a free sample offer to get customers onboarded and to capture credit card info. A customer will pay $5 for shipping, and we'll send them (1) bottle (1) lid and (2) cartridges. When a customer signs up for the free sample offer, we automatically roll them into an 8 cartridge/month subscription, which ships 10 days after the sample is shipped. This subscription will be reflected in the customer’s cart when the checkout for the free sample. The 8-pack that that is sent by default is one SKU. This is unique as all other SKU’s represent 4-packs as outlined below. 3. Customers who purchase a subscription must be able to pick their flavors packs. Cartridges are packaged in quantities of 4. A 16-cartridge subscription will need 4 flavor options, 24-cartridges will need 6, etc. 4. Subscriptions are currently offered in multiples of 8 for fulfillment reasons. Subscriptions of 8,16, 24, etc. cartridges will be offered. Ideally, our solution will provide flexibility to offer subscriptions in other quantities (12, 20, etc.) as well once we’ve solved for them on the fulfillment side. 5. There are two ways to achieve this: Create subscription SKU’s based on quantities e.g. 8 Cartridges/month, 12 cartridges/month, etc. Create a “Build Your Subscription” user flow. Step 1: Choose your quantity (a multiple of eight - 8, 16, 24) & Step 2: Choose the flavors options. 6. The price per cartridge of the subscription decreases with quantity. An 8 cartridge/month subscription is $25. 16 cartridge/month is $40. 7. In either case, we need to push the order data to our 3PL as flavor quantities. A 16-cartridge subscription get's pushed to them each month as a regular order with 4 flavor packs. 8. A customer should be able to edit their flavor pack selections from their admin. 9. A customer should be able to edit the subscription quantity from the flavor area. 10. A customer should be able to pause their subscription. 11. A customer service representative should be able to easily adjust a customer’s subscription from the Cirkul Admin panel. Question: 1. Have you previously built a recurring order solution? If so, please provide examples. If not, why are you confident that you can complete this project? 2. How long do you estimate that this project will take?