Personally I don't like of a large number of small datastores, I prefer start with something like 2TB datastores... but since you have a very small environment, maybe 4x1TB datastores will be a good design... and if you have Enterprise Plus license, just create a datastore cluster and place all datastores on it.
Using Storage DRS on vSphere and the Automated Data Tiering feature of storage will gives you great storage service level and avoid bottleneck and the strategy (at least for non VDI workloads) of place OS and data on separated datastores no make much sense.
And about use snapshot, I think you will need a snapshot manager to make use of this feature... since I'm not a Dell shop, searching on the web I can found the following: How Dell EqualLogic Auto-Snapshot Manager/VMware Edition Helps Protect Virtual Environments | Dell