We have a DIY pond with a bog - built it when nearly every pond pro told us it was a big mistake. Have never regretted it. Ours is 4x6 and 4 feet deep. Centipede, snorkel and lots of rocks and gravel. And simple answer is yes - bigger is always better. Build the biggest you can fit and afford - not once have we heard anyone say "I wish I had built a smaller pond".
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@GBBUDD mentioned, we did have a pro come in last season and re-work the waterfall - had some issues with construction that eventually caught up to us and lead to some water being diverted out of the pond. We loved what they did so much to fix that issue that we had them come back and rebuild the rest of the waterfall and it's amazing.
One thing we did find is that, while we had great biological filtration with the bog, and great mechanical filtration for the large debris with the negative edge, the fine, floating debris eventually got to be more than what we wanted to see. We used a box filter as a supplement and found that to be very helpful, but not aesthetically pleasing to have sitting next to the pond. So when they were re-working our waterfall we had them add a Biofalls for the fine filtration. It's been a brilliant solution. So I guess the moral of the story is a pond doesn't have to be bog OR Biofalls - there's room and purpose for both on a pond.