You're using the wrong version of the installer. The one you are using is the one for CC3, not for CC3+ which is what you have. You'll find the right one on your registered user download pages.

Not sure why you're referencing DRM here though, a technical issue like this doesn't have anything to do with DRM. This is just a compatibility issue where CC3 add-ons can't be used with CC3+ and vice versa, not a protection scheme.

I have a couple of videos on creating symbol catalogs which may help:

vthumb(dRRa6ctWPJY|Creating Symbols - Part 1 - Finding and Preparing Images)

vthumb(cYxAIPa7dak|Creating Symbols - Part 2 - Creating a Symbol Catalog)

Doing a map of that size isn't a problem in CC3+. But it will be a bit time consuming, a map like that is not done in an afternoon.

Since you're mentioning the isometric Schley city set, i am not convinced it will be appropriate for such a large city. I haven't tried, but the isometric sets are generally better when you can see the details a bit more clearly. Might be a good resource for mapping closeup of individual districts for example.

Personally, I am not convinced it is a good starting point doing such a large map if you are unfamiliar with CC3+ though. I recommend starting with something simpler to get some experience first, or it is likely to be overwhelming.

You might want to have a look at this live stream recording where Ralf starts making a small city. Far from the size of your desired city, but shows off the tools and techniques.

The effect employed here require it to be a polygon, you can't do the same with a line.

One way to handle this is to just let the poly extend beyond the border of the map. The part sticking out will be hidden by the map border and the screen. The end result should be that it looks like a line.

The only difference between regular image exporting and rectangular section is that after you have clicked save in the save as dialog, instead of starting the export immediately, you will be prompted (on the CC3+ command line) to pick two opposite corners of your export (by clicking your mouse in the drawing or typing in the coordinates, either works). CC3+ will then export only the parts that is within the area defined by those points instead of the entire map.

The export process is explained in detail with images in the user manual, starting on page 47.