That is awesome man, i only have a 32" long fish tank and upgrading to a 4ft fish tank which i have the tank but looking for a hood and white sand. I know you think you may be crazy which you seem lol but still not as bad as my relative in Britol, he has already a 7ft marine tank in his wall inbetween his living room and kitchen.
Now he has almost finished his second project where he has extended his house single floor attached to his kitchen and has built a 8ft by 8ft fish tank in there which is sick. I don't know how high it is gonna be but will be a really good marine reef for the fish comming. He has finished fitting all the pipe works and needs to buy the water. There will be a big glass window in the kitchen where you can see inside and even has built in cameras for a peek inside. I don't know if anyone's heard of it but there is a new product out where you can actually control a little camera that can swim around the tank which will be wicked and he said he is going to get one for when he goes to work and on his website he would be able to see a video through the cameras swimming. It would be helpful to see around the deep areas of the tank and under the coral.
I'm sorry i got caught up in the moment with that lol
I have some suggestions for what you can stock, i was thinking you could go to the oddball side and for your really big fish get some oscars and fire eels, and if compatible a huge mbu puffer for the 6ft tank. As different types of fish makes it fun and relaxing with fire eels and other spiny eels and puffers which i think most people love as they are different and cute. I have a small cute green spotted puffer at the moment and hoping to buy one more at the moment.
Another fish would be nice as well in the 6ft for the bigger fish would be a stingray as they are different and really nice, they come up at top of the tank and you can stroke them and even hand feed them, inlcuding the fire eel when they are at around 20"+ which are best.
Hope you send pics and that everything does turn out well