Advice wanted for tank move and new build

[SteveConn]

I'll be moving into a house in a months time. No more restrictions of living in a condo! The tank will go into the basement at the new home.

I currently have an awesome 75g eurobraced tank built by Concept. For the transition to the new place I am looking for either a large, cheap tank to hold the rock and coral for up to a few weeks before settling in the display tank OR:
Large plastic tank that can hold about the same volume but preferably 2' or more wide (I'm looking for surface area more than depth so I dont have to stack my existing rock too much)

Once I get settled in to the new place, I want to start upgrading to a larger tank. I am already maxed out for space for corals after being in the hobby for 1.5 yrs and I am interested in fish that need more swimming room such as larger tangs.

Is 6 ft long by 2ft wide large enough or should I go for 7ft?
I'd prefer not having a depth greater than 2 ft to allow for easy tank maintenance and placement of corals.
I am also wanting to add a frag tank.. thinking 3' long x 2' wide x 14" deep. Not sure if it should all be plumbed together.
Also debating if all the plumbing and sump should be behind a wall.

Very open to feedback from the forum. Thanks!