Hi ehawkins, welcome to the forum....

In regards to your pier blocks....I'd go with 'overkill'. If something were to happen...well that would be a mess...

I saw a guy tie 4 of the mixing tubs for concrete, together with one extrenal bell siphon. He had a pretty large fish tank...so the water level didn't go up and down much.
Not sure how big your beds will be...? You have to think about how much water the beds will be using from the sump/fish tank while they fill up.