Are you planning on heating the basement or just letting it find its own temp? I'm not sure exactly where you are and how cold the basement will get, but having a large volume of water someplace where you have to heat it drastically could add up, so you may want to think about how to distribute the volume upstairs vs basement. Fwiw if you're doing the carpentry, it could look pretty nice with a refugium above the main tank, perhaps a 30 breeder to match the 65 in footprint. Makes the trim work easier! Think about a floor to ceiling column with the two tanks built in. Just make sure you have an unobstructed opening of at least 14", preferably 16" above the main tank, most preferably on both sides of the island. You may walk a bit more, but you can probably avoid serious contortions!