here's a quick slap together of where stuff will sit. Still not too sure how I'm going to fit stuff in as most of it needs to be near the 2 foot tank (sump) I will probably dose the calc reactor straight into the refugium instead of the sump as there is more room. The main things that HAVE to stay as they are are the location of the refugium and sump as I want to minimise the length of the return. The red arrows show direct of flow out and in from/to the main tank.
The refugium will have an overflow to feed the sump (hence the variable height bench)
I can basically plump up a tap (for RODI and top-up water tank) and electrical points (most of which will be mounted higher than the tanks at this stage) anywhere.
I also bought a 2nd hand laundry sink which I will probably sit in between the 2 and 3 foot tanks to allow ease of water changes. Most pipes will be plumbed up with taps to direct water flow "to the main system" or "to the sink" meaning that removal of water from the tank is as easy turning a tap and adding NSW back is as easy as turning on a pump.
Chiller, Calcium Reactor, CO2 bottle, Kalkwasser tank etc etc will mostly be located below the bench (will this be a problem?) so it's easy to access.