Can’t really help on sumps as only seen them, not used them but was thinking it was just convenient as well. I’ve never seen a dual sump but that I think is a very big tank.
I’d be tempted to leave all is unless going bigger on the sump. I’d say it all depends on stocking but everything I’ve seen is you want the water volume as big as possible.
I only have 150gal
FW and use a 3gal and 5gal canister filters. I don’t need both but I hate dragging one outside to clean, filter cleans can be very good since I alternate cleans, etc. So for me it works well. Only time I think not go bigger is when not practical to work in.
On lights, I’d go LEDs but
SW people will know more. I’ve used reef box lights in planted tanks which did have (computer) fans so could be worth leaving the lighting system fans just as is for moment.
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