Lots of tanks have side and back return holes, typically you don't have to worry about creating weak points as they don't usually go at the weakest point of the tank.
A surge is a waste of time for a 140gal, once you hit 500+ it starts to make a little more sense.
I'm not sure how you plan on setting up a gyre flow pattern with the return, typically this is done with two closed loop systems each pushing and pulling in opposite directions of the tank so you run them on interval timers. This way you'll have flow pushing one direction for a period of time and then switch it to flow the other way. Also you can size a closed loop pump to pretty much any size you want so I fail to see how it would be overkill.
Why not just run a wave box? You could even build it externally to avoid seeing it within the display.
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