Start with one or two. Plan on making up a nuc during your main flow. You can decide if you want ot buy a queen or use one of the queens from one of your hives or do a walk-away split.

Concptually all mediums sounds good. It is nice to have only one size frame. you can mix and match as you please then. One limitation is that most other beekeepers use deeps for brood chambers at a minimum. It can be hard to find medium nucs. You can always use deeps for brood chambers only and medium or shallows for supers.

I started out using deeps and mediums as I mentioned above. I'm moving more towards using deeps for brood chamber and supers. I will still use some mediums for supers. If a deep full of honey is too heavy for me to lift I can just pull a few frames out and then lift it. I don't have a lot of hives so a little extra time is not a burden to me.