Materials not updating in realtime / Mac Pro 5.1 setup for new blender user

I hope someone can point me in the direction of the correct way to move forward.
New to Blender and just finding my feet, I have installed 2.8 on my Mac Pro 5.1 (32GB, 3.26 GHz 6 Core) using a GTX 780 3MB card.
I have noticed that materials do not update in realtime. To see any results I need to re-load the saved Blender file. This is the case for HDRI backgrounds too.
I have been reading about Cuda and checked in Blender preferences, it doesn’t find any Cuda devices so I assume this needs to be installed. Correct? If so, what does this help with?
Is this the correct method to install it?
Cudu installation guide
Is there anything I am missing or that I need to configure in order to get the best from my current system?

Any advice hugely appreciated at this stage and sorry if there is a post that already explains this.
Here’s a screenshot of my 1st attempt at a scene (with the help of tutorials and some free materials etc.)