Rob, your post asks if a rebar grid every 4" was overkill. If you really meant every 4 INCHES, by all means yes; that's overkill. A common rebar grid would be more like every 16".
Since the rebar will be traveling slab to slab in planted areas (not completely encased in concrete), you'll want to use the coated rebar which resists rust.
A question I have is the security of the interconnecting beams; I'd expect these to crack unless deep control joints are made where they connect to each slab.
If your not using fiber-mesh concrete, I'd definitely use wire mesh in each slab, also.
Sounds like a good looking drive, Rob; good luck.
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