There is a hatch in the middle, but it means removing the middle buildings for access. It's not something I can do every day, as I normally knock over a few things in doing it. I am building the modular police station which will go between the diner and assembly square. Once that's done, I will finish the corner section and move out from there. I'm also designing a modular train station to replace the current MOC.
I have been pondering getting some trans blue and white to give the appearance of the depth of the canal but the cost was stomach-churning.
I'll check out the minifig deal, thanks!