I say go big sump w/ canister(s), heaters in the sump and pool filter sand.
One thought (never kept rays so just opinion here):
You to keep up with rays bio you will want allot of turn over going over your media. You could always hook up one of the canisters inlet to the sump and have the outlet/spraybar going over your drip tray. I did this on my brackish setup to get even coverage over wet/dry towers drip tray.
Plus when you turn off the flow going to your sump for WC's, you can leave the canister running over the media and not worry about it drying out. A tank that big with rays would take some time for do the big WC you would need to do.