I really like your ideas and in Civ 5 venice was always my favorite civ to play but its a bit buggy still,
For some reason i'm not able to place the bacino on ocean coast, i could only place it on lake coastal tiles,
UI bug: in the ressource screen it shows your towns as if they had the -30 happiness penalty (they dont its just visual) note that i started in antiquity with rome augustus and interestingly the city state Babylon i bought doesnt show the -30 pen but all the other former cities and towns do
The Bacino is supposed to be placed on dry land adjacent to a Coast tile (and not adjacent to another Bacino), perhaps that is the cause of the placement issue? I've noticed that it needs to be placed on an existing rural district, so you need to have already been working it. I'm unsure if this is intentional behavior for custom improvements in Civ 7 yet or not (haven't paid too much attention to it), but I'll look into it.
Regarding the UI bug - good to note about the happiness penalty. Just to confirm something - Babylon was purchased in the antiquity age, correct?
Either way, I'm glad you found the ideas sound! I appreciate the feedback - will get a fix out shortly with this!