OK, so this is relatively complicated, so bear with me.
To run Radion lights, you only need to program them once with a USB cable. That's the bare-bones, set it and forget it approach, nothing extra required. I think this is correct, but you REALLY need to call BRS to be certain about this, since I don't run mine this way.
The second option is with Ecotech's reef link gizmo. That gives you wireless control of Radion lights, Vortech pumps, and now Vectra pumps from an app.
The third option is with the Neptune Apex tank controller. To do this, you need the Apex controller and the WXM module. I can't verify whether the Vectra pumps will work through the WXM module, but the Radion lights and Vortech pumps definitely will.
As far as what Apex to get, there's a $799 package that contains the controller, 3 probes and the controllable outlet & i-link power supply. The $499 ApexEL ("EL" stands for "entry level", I think). That controller is not identical to the first one - it deletes a variable voltage output (necessary for controlling Tunze pumps), the salinity probe and the ORP probe connection. I think the deal with this is that you can add back all of that capability later on by purchasing modules (in this case, the VDM module, the Salinity module, and the pH/ORP module). So lower up-front cost, but higher long-term cost with more wires and modules.
For controlling Tunzes from the Apex, you need a specific cord that plugs into the Apex "pro", or plugs into the VDM module if you have the ApexEL. The other end of that cord plugs into 2 controllers that come with a pair of Tunze pumps. You can then run the pumps through the Apex with waves, surges, etc... The other way you can do it without the Apex is to buy a specific Tunze cord that hooks a pair of the controllers together. That will give you sync/antisync operation - when one pump is running fast, one pump will be running slower, and vice-versa. You can, of course, adjust the high and low speeds of the pumps.
I guess this is what I'd say about bigger tanks. They're easier to keep stable, but since you've got a good deal of reefing experience, I doubt that would be an issue for you. The great thing about a big tank is bigger fish, and more of them, plus plenty of room to aquascape. The downside to a big tank is more seawater for water changes, much more expensive lighting if you go with LED (for T5HO or MH, not quite as steep a price hike), and possibly, a much bigger PITA if you're changing water with buckets.