185 over a 206 for sure! Same engine on a slightly skinnier fuse = performance (well, relatively speaking).
Operating either on open water is far from ideal. A beaver will take conditions that would see a 206/185 throwing bracing wires and spreader bars.
If you stay within the protected bays then you should be alright, but I'd still go the 185 over a 206.
MQX is also an amphib so there goes any real hope of payload to make a profit. Plus with your experience (or lack there of), getting insurance on an amphib will be near impossible, regardless of whether it's a beaver or a 206.
Now if you want to burn cash a little more slowly a 172XP is always another option. Bill had operated many a 172XP and if memory serves me correctly so did Akuna. You'll have to fill less seats to turn a profit and burns less juice than a 182.
I'd talk to Bill Lane though on true operating economics of each of the 172XP, 182, 185 and 206, he's operated them commercially for decades so knows what he's talking about.
Though I'm sure given that you've got a business plan and have been talking to the banks you've already employed the services of an experienced consultant to get true operating costs for your financial forecasts.
Don't fall for the trap of "I want to get the biggest plane I can afford".