I like the plan Tom! Just wondering why the equal size drains and returns? If I could change one thing on my new tank it would be the drain size. How many drains are you planning ? Ya might want consider 1 1/2 to 2 in for the drains. It will make flooding less likely,allow you to install larger pump in the future if you deiced you gotta have more!
It also makes much easier to make the noise reduction much better. Have you considered theRed Dragon series pumps? Huge volumes with very low wattage consumption and are practically bluet proof! And have a very small footprint. Little pricey but worth it in the long run! Following along for sure ,you could do a hot water heater heat system if your hot water tank is close by. Dave(diver down) did this on his system and really reduced the expense of a 900 gallon total system