I'm starting a new project where we are expecting to migrate desktop based Access 2016 applications (with a lot of backend VBA and relationships between the tables) into SharePoint 2016 on-premise and very soon, SharePoint Online. From what I've been told, we'll be given site permission to a SharePoint site that we can do whatever we want with. I am hoping that with SharePoint 2016 on-premise and eventually SharePoint online means that there is a SQL Server and eventually Azure SQL Database that I can migrate the Access backend tables and queries, as I know SharePoint lists will be inadequate for this, despite the false notion that SharePoint lists are an equivalent substitute for database tables. 

My concern is how to build the custom forms, perform the needed business logic, perform CRUD operations, and upload data in the form of Excel files from the SharePoint site to the backend. 

I'm new to SharePoint and given that it does not support VBA, that Microsoft cut out Access Web Apps earlier this year, and they are phasing out SharePoint Designer 2013 and InfoPath, some research over the past week indicates my best options are building custom web application using ASP.NET Core and somehow deploying that to the SharePoint site and subsites that we have control over, or developing a lot of HTML, CSS, and JS to create the front-end interface. I had read about the Business Connectivity Service to get and post data to / from the SharePoint site front end and the DB backend, as well as using Javascript and AJAX calls to do CRUD operations between the database and the frontend. I looked into PowerApps and those seem insufficient, and I'm still trying to distinguish between SharePoint web parts and SharePoint add-ins.

Is any of the above even a feasible option? Could someone chime in on a better path to go about this? What technologies would I need to best go about this?