Hi, i reviewed your brief, and i have a proposal for you. I'd prefer not to divide your digital backend to the site AND mobile app. I'd combine it to the site only, which will utilize mobile template and will be accessible from EVERY device. And if i ran your business, i'd use Adobe Business Catalyst for that. Why? It already has all the features you need, tons of features, including CRM, API integrations, and custom web apps engine. If you will hire me to maintain it, it'll cost you about 200 to 500 USD to develop (it depends on the functionality we can discuss before you award, it's free). And a 70 USD per month for hosting and support fee. BC hosting is very fast and stable. And you can apply additional functionality further, very fast, and at low cost. And i will always be in touch to help you if you have any questions or issues with your online business. If you've got any questions, then get back to me and let us discuss this all in details. Thanks.