Build and Edit Online Laundry Service Store

We need an e-commerce site developed. Its for a pick-up/delivery laundry service. Users can come to the site and sign up for one of the monthly plans. These plans allow for a certain amount of pounds of laundry cleaned and folded every month. There is also a pay as go option. We also offer college plans. We have a working front-end for the site but we need the back-end developed. We would like it to be with an existing e-commerce platform such as opencart. Something that is easily managed from the back-end. The payment gateway is going to be USAepay, so the awarded developer must have experience with this payment gateway. The process works like this. A user signs up for an account. They can either sign up for one of our monthly plans or they can do a pay as you go feature. Right now we offer three monthly subscription plans. These plans vary in poundage and price per month. The monthly plans allow for a certain amount of laundry picked up, washed/folded and delivered back to the users doorstep. The monthly plans require a reoccurring fee every month. If a user exceeds the monthly poundage of their plan then they are charged an overage fee. These overages have to be automatically calculated in the back-end when the admin enters the weight of a users order. So once the admin enters the weight of a users order it should subtract the amount of pounds from the users monthly allotment. If they don't have a plan it should charge them, per pound, at the standard pay as you go rate. If they have a plan and are over their monthly limits it should charge them for the remaining pounds not covered by the plan that month. We need an easy, efficient way for the admin to go through the days orders and enter in the poundage for each customer. Once the admin hits submit it needs to automatically calculate if there are any overages and invoice the user. The pick-up laundry service also offers dry cleaning services. The user must be able to specify their order type in the back-end. Conversely, the admin must be able to add the price of the dry cleaning order in the back-end as the cost will be calculated in house and not through the site. Say a user has a monthly plan and also wants to add dry cleaning onto their order, the admin has to have a way to add on that amount. Users must also be able to access a dashboard from their account where they can schedule a pick up, sign up for a plan, see their order history and update their user information. Alot of these internal pages exist but we need to have integrate them with the new e-commerce back-end. The admin must also be able to login into a users dashboard from the back-end in case they have to assist the customer with their order. I have attached a preview of the existing site to demonstrate the monthly plans and concept. If you have any questions please let me know. Must be developed on our servers.