How to minimise storage consumption?

You might want to check out some hybrid file servers, one offloading cold data to public cloud where storage is cheap (S3) or nearly free (Glacier). If you have Enterprise agreement in Azure you might want to try StorSimple from Microsoft, both physical and virtual.

https://azure.microsoft.com/en-us/services/storsimple/

Nasuni is also nice, but doesn't have reliable SMB3 so far.

https://www.nasuni.com

There are a lot of interesting solutions on the market, I haven't tried Nasuni but looks like a fit. Also, you may take a look at Aclouda which can be used as a hardware gateway and present cloud storage as a local drive and offload data to the cloud automatically. It can be installed on a local server as SATA/SAS drive with connectivity to the cloud either Amazon or Azure. http://aclouda.com/

Since you have a considerable big amount of data that do not change much with time I would highly recommend you implement some kind of tiering (Storage Spaces with automated tiering should fit). The idea is that the "hot" tier, which is local storage should contain most recent data that must be accessed quickly and the "cold" tier can be offloaded to the cloud.

The idea is not new - Nasuni https://www.nasuni.com/ does stuff very similar to this approach. A DIY option is S3Fuse https://www.interserver.net/tips/kb/mount-s3-bucket-centos-ubuntu-using-s3fs/ that allows you to mount a cloud storage as a local drive. StorSimple https://azure.microsoft.com/en-us/services/storsimple/ is another choice but it is strictly bound to Azure.

If you are not willing to install/configure and maintain any additional software you can go with a hardware gateway like AcloudA http://aclouda.com/ that will do the job without requiring any additional software or drivers.