What's up with the flow

You wont need a buffer tank with your setup, it looks like you have a CR240 which turns down (modulates) to 17,000 BTU minimum, and there is enough mass in the piping heatbox and demand in the tubing to not warrant that. Buffers are mainly used when heating loads are smaller than minimum firing rates resulting in cycling of burner.

While 5 zones is mentioned it appears they are not controlled, it is probably more like 5 loops into 5 different areas.

Buffers never hurt, but experience tells me here its not really necessary here

They are not controlled at this moment but will be when I get this sorted out. Probably there will be 3 or 4 control zones, depending on how I want to the basement.