Opencart/Joomla - Member Subscription System repost

My client is in the tea business and they intend to sell tea products online (e-commerce) AND deliver tea products to subscribers. We will be using OpenCart for the e-commerce shopping cart (to be done by our side). *** Note: Joomla is acceptable if the process is easier. ** We need someone to create a MEMBER SUBSCRIPTION SYSTEM which will INTEGRATE with Opencart system. *** Description of Member Subscription System: (i) Users can sign up for subscription packages e.g. Plan A, Plan B, Plan C Example: - Plan A - users pay $10 per month - Plan B - users pay $20 per month - Plan C - users pay $30 per month - They can choose to pay monthly, quarterly, 6-monthly or yearly. (ii) Once users subscribed, the $amount paid will be stored inside their member account. This amount can be used to select different types of tea leaves. * Note: Members can choose to use up the whole amount in their account at any time. Unused $amounts are stored in their member area. (iii) In the Member Area, users can do these: a) Select tea leaves using their stored $amount b) Upgrade or downgrade their subscription plans a) There are different types of tea leaves which users can choose at any time e.g. Grade A, B and C tea leaves. Example: - Grade A tea leaves is worth $3, Grade B is $2 and Grade C is worth $1. - Plan A subscribers (who has $10 in their account) can only select 10x Grade C tea leaves (total $10) OR 3x Grade A & 1x Grade C tea leaves (up to $10 worth). - If they have $100 in their account (for example), they can choose to use up the whole amount at one time or just part of it. b) Users are able to upgrade or downgrade their subscription plans. The amount difference will be added/deducted from their $amount credits. Example: Users who subscribed for Plan C want to DOWNGRADE their plan, and the remaining balance will be stored as $credits in their account. (iv) Once users select the tea leaves and submit, Administrator will receive the orders and deliver the tea leaves accordingly. ******************************** For admin: - Can modify members' plans - Upgrade or Download members' subscription - Download Excel report which contains members' subscriptions AND the types of tea leaves selected every month *** Important Please note again that we will be doing the e-commerce portion for this website. Awarded Freelancer is to create only the Subscription System. PLEASE GIVE A SUMMARY OF WHAT YOU UNDERSTAND. SUGGESTIONS WELCOME.