Considering this is a generic underwater style, and not made for a specific setting, I think it is safe to ignore things like breathing, just assume that any DM who is using an underwater style have a way in the system they are using to handle that issue.

Those tools are using hatch style fills. These are separate files that lives in the @Hatch Styles folder. These are regular CC3+ drawings, and you can go in and simply rescale the entities in the fill file.

To avoid messing up the default tool, I highly recommend that you make a copy of the files you wish to change and then modify the copy.

Then, make a copy of the drawing tool in your maps as well (:CC2DRAWTOOLS: -> Advanced), and change the Outline of your copy of the tool to use the new fill you just created.

Looks good. But yea, it's kind of wrongly shaped. The building is also a 3-storey building, so I would expect some visible stairs somewhere going to the other floors, even if not mapped.

Also, since this is an inn, shouldn't there be some kind of reception/bar to find the innkeeper? Or maybe you left it out intentionally.Or maybe I am blind.

Sheets are drawn on screen in the order listed in the dialog, so the very last sheet in the list will come out on top. Normally the text sheet is almost last, but placing it last should guarantee that the text is on top.

Check this FAQ entry, it should help you: