Independent Platform Communucation Architecture

I need an advice about independent platform architecture design.

My scenario is about presentation 3D data on browser to customer using UE4 or Unity3D. I prefer UE4 but Unity3D also works for me.

We have a server doing some computation about 3D objects. After this server finishes it's computation it creates mesh data (vertices, faces...etc) and some other data too.

After server done generating mesh data and report data I need to present it to customer. 3D presentation will be using Unity3D HTML5 or Unity Web Player or UE4 HTML5. This presentation will be hosted on our web page.

User must login to our authorization system on our web page. Then send us his/her raw data. Our server or compute cloud process the data then save the processed data to a database or sth else. Server also send an email to the customer when to give information that his/her data is ready. After that customer will login to our web page again and open the html5 app written using Unity3D or UE4. The html5 app need to reach the user related data.

I have no experience about web. But with some search I've informed a bit. Which aproach must I prefer? Directly accessing database, web services, php rest...etc?