Conjoining two tanks DIY

[Reefer's Paradise]

Hey all,
So I am planning on joining two tanks together. I have a frag tank 24x12x8 and a AIO cube 12x12x12.
Now my first question is mainly opinions on how you would join the two?
Here's some info:
AIO is acrylic and is a "show" fuge if conjoined, if not it's a macro tank lol, other tank is rimless undrilled basic frag tank low iron.
My plan or thought is to install an overflow type set up in the back of the AIO first chamber of two and have gravity fed to the frag tank and a pump to send water back to AIO second chamber or fed directly back to the tank. Now it's not a big drop for gravity feed but I am thinking of drilling a hole adding a bulk head and piping at a 45° to the lower tank which is 5" shorter. Almost the same concept as the CPR HOB Fuge but piping at a 45° angle instead of straight up and down.
Other option is of course a siphon overflow box and return pump but with lots of worry of failure and overflowing I wouldn't like this as my first option even with high end pieces for the job and alarm/shut off back ups. Also more money!
Let me know your thoughts!
Here's a pic:

 

[MasterBacon]

Maybe add a sump below all and have each overflow down to the next then to the sump with return back to the AIO.
AIO- FRAG- SUMP-Return to AIO waterfall effect.

 

[Squirrel_reefer]

I would just be leery of the fact that the AIO is much taller than the frag tank, connecting them into one system is def not impossible but if any gravity fed system between the two failed you're gunna have a wet floor when it drains into the frag tank. If you're going to gravity feed into the frag just put the drain really high on the AIO