I'll echo some of these points too. I shot a series of Canon point-n-shoots in matching Canon plastic housings - never had a housing issue with any of them. Eventually I wanted to 'move up' as I felt I already had all the decent shots I'd get from a point-n-shoot without strobes. So I moved onto a Sony RX100 ii in a Nauticam housing. I'll echo the point about housings being a system, though in my particular example not so much. I outgrew the Sony in a year (slow focus) and then moved on to (finally!) putting a good camera underwater, meaning a D810 in a Nauticam housing. I simply moved the two strobes and strobe arms and focus light from the Sony to the Nikon rig, needing only to get new fiber cables. Since then though, I've moved to a Nauticam D850 housing and now a Nauticam Z9 housing. The 180 degree viewfinder I bought with the D810 rig is still used on the Z9 rig, along with the strobes, and the 230mm dome port. Different lenses meant changing macro port and dome extension, but all the ports and bits I bought for the D810 rig moved on to the D850 rig.
On the egonomics question - you don't know it yet, but there are ok and better ways to push buttons underwater. You need to not overload your right hand in particular, and they may well mean NOT putting a housing button directly over a camera button. A great example of this is the Nauticam Z9 housing. I have three function buttons on the front of the housing, each set to a different autofocus type. On my housing, the Fn1 button is turned into a conveniently-placed lever for the right hand. But the Fn2 and Fn3 buttons are both assigned to a rocker lever on the LEFT hand. The playback button, which is actually located on the right lower back of the camera gets moved to a lever on the top left of the camera. There are a series of levers and rods inside the housing making all this stuff happen.
Buoyancy - potential issue with any housings. Some (Canon compacts) had an accessory weight kit for them. My big Nauticam rigs are quite negative in the water, but last June I learned how to balance them out. Simply hook a luggage scale to them (carry handle is good) while the rig is sitting in the (salt) water. I had four old Stix floats on my strobe arms and needed to add four more. Now the rig is almost perfectly weightless in the water. I can balance it on the end of a pinkie finger or just let it go and watch it stay in front of me. You want any underwater rig to be in that state or close to it. Unfortunately, the big dome port pitches the camera straight up, so I really need to add some tire weights or some such to trim the rotation out too. The macro rig with the much smaller macro port needs additional floats as that small port doesn't hold much air to float the rig.
Finally, resale. Like any big purchase, the key to doing well in resale is to buy cheap, not to try to sell high. So if you can get a good used price on a popular Ikelite housing, you should be able to resell it at reasonable cost. But some of this stuff is also hard to resell. And you might not get the price you wanted either. I thought $1700 was a good price for my used NA-D810 housing, but it turned out to be too high for my only bidder.
Finally, there is one option that really isn't optional, and that is a vacuum leak detector. Any housing you get should have one. That might contribute to a higher price on one housing compared to another.