Looks like the entity is simply too complicated here because of too much fractalization of the walls. The existing entity has 32632 nodes. That's bordeline what the tools can handle.

I recommend you reduce the node count of your entity somewhat. Try using the SIMPLIFY command on it (I suggest trying with a simplification distance of 0.1), this should reduce the node count significantly.

For your particular map there, you'll also need to consider how to handle "holes", (i.e. solid walls in the middle of the map). A standard CC3+ polygon cannot have holes in it, which you seemed to have noticed by the area up near that entrance to 10 not being closed properly. This is something you probably should consider right now before doing any more work.

There are three ways to handle holes. The one is through the use of a multipoly, where you draw the base floor only following the outer outline, and then you draw the inner walls as their own polygons and merge everything together using a multipoly. This works, but the multipoly cannot be edited by the drawing tool edit command once joined (without splitting it up again, then editing, and then joining it back together), so this approach works best if you plan for this and do the actual outline first.

The second way is basically draw the inner walls as their own polygons on top of the floor, usin an appropriate filling for the walls, and just accepting that the floor doesn't have holes where these walls are, but instead a wall covering that part of the floor.

The third way is through the use of the color key sheet effect. As with the other options, the main floor needs to follow the outer outline of the floor, and then all the inner walls are drawn in a distinct solid color on the same sheet as the floor, and the effect is used to "knock out" those parts, creating the visual appearance of holes.

You can use the macro commands GOLAYER and GOSHEET (or LAYER and SSET if you prefer an error message instead of creating a new layer/sheet if it doesn't exist)

Using them by themselves may not speed up things too much since you need to specify the name, but you can then define your own named macros using something short and easy to go to a predefined sheet directly. And if you want the same command to just go to the next in a list, you should be able to set that up by using a variable to keep track of state and then using a conditional to activate the next sheet.

You can also add your macro commands to the CC3+ menus. This allows you to easily activate it from a menu, but maybe of equal interest, you can add shortcut keys to any menu command. Read more about menu editing.

Lastly, you can also use the SNEXT/SPREV to go to the next/previous sheet in the list. (There's no equivalent for layers)

All the selection options have shortcut keys, but they are only active during the selection procedure, i.e. when the CC3+ command line reads "Select Entities".

Selecting everything is just A (for all)

What Sue talks about isn't buttons, but the context menu you get when you right click inside the drawing area during selection.

More about selections.

Don't you know what happens to people asking such questions? (If not, ask Sue)

Both @Wyvern and @DaltonSpence raises some interesting points about scaling here, and the critique of scaling in a map.

Personally for me, (A)D&D (and several others) have always been about a medieval setting with a twist. The introduction of magic and adventurers change the picture somewhat, but for me, these people have always been a kind of privileged people. Not everyone is a magic user, or even know a magic user. A town may have a town church with a few clerics and a town mage, but these few people doesn't significantly change the town outside their own abode, they have their own things to worry about, and their services are expensive enough that the average peasant/shopkeeper/innkeeper/smith/hunter/etc can't afford their services just to make simple things easier (like building a house that defy the general medieval technology level). Adventurers find treasure and bring in money, but while it may make the adventurers rich, it isn't that much divided over a town, making their contribution minor as well. As such, I've always felt that anything not adhering to medieval standards is "wrong" unless there is very good reason for it (and not all innkeepers can be ex-adventures who retired with both fortune and magic). And thus I've felt that a lot of the buildings from official sources are just plain wrong, either just because they are more focused on working as a battlemap than being a true building floorplan, or because the original designer was just ignorant of the subject matter. It just feels wrong when a common single-bed room at a common inn is larger than many people's living rooms in modern times.

Of course, many people will disagree with me here, one told me years ago that he didn't see anything medieval in D&D at all. Some people think I am horrible boring, and think it is much better when the world is filled to the brim with the fantastical. This is of course a matter of opinion. I find that I have more fun when the fantastical is rare, and the world itself is "as medieval as possible" within a realm that after all do have magic users and dragons. But the fact that I prefer one style doesn't make the other viewpoint less valid. Whether you made the map because that's the way you like it, or because you're trying to stay true to the source material doesn't matter. If you end up with what you were trying to do, then it is a good map.

OK, that turned out to be a longer rant than expected. What I was trying to say is that I find these aspects of critique both interesting and valuable. Not just for the actual mapper, @Dak in this case, but also for others in thinking about how your map should look. Some critique may or may not be invalid for the current mapper, but are still valid points to make in a more general sense.