>> like this to work, ideally so successfully that it keeps scaling up.

There are hard scale issues. The wings must remain close to the water for ground effect to be a thing. But the thing still needs to bank to turn. That means one wingtip getting higher to the point it can lose GE lift, and the other lower to the point it might strike a bigger-than-average wave. The longer the wings, the less the craft can bank in a turn. Get too large and in-ground-effect flight becomes impractical/dangerous.

Good concerns honestly.

I wonder how much turning you could get just from adjusting motors. Especially if each of those 12 motors can individually adjust, I'd imagine you could get some decent yaw.

Also as per the quote which helpfully points out, WIG is typically flying half it's wing height. Since wingspan and altitude are thus linearly corresponded I'm not not sure (not convinced either way) that there's a problem (or not) from wingspan.