Correct aspect ratio compared to the paper size you exporting to. For example, if you have a 1000x800 map, your aspect ratio is 10:8, but a standard A-size paper is closer to 10:7. So if you just blindly type in 297 mm for both dimensions, the exported image will be 297 by 237.6 mm, which is larger than the 297x210 mm of an A4 paper. (I didn't account for margins here)

CC3+ automatically calculates the other dimension based on the aspect ratio of your map, not the paper.

Of course, if you don't mind it getting a bit large and simply resize it down to fit the paper on print, then using the largest value works, but if you want it accurately, then you have to actually make your map in the right aspect ratio from the beginning, or you need to also calculate the lesser value so CC3+ can export an image that fits within both the dimensions.

Keep in mind that using the largest measurement for both only works if your map is in the proper aspect ratio starting out. But if you make a square map (or any other map that doesn't have the correct aspect ratio compared to the paper aspect) that you just want to fit into the paper, you'll probably need to use the lesser of the 2 measurements instead, otherwise it won't be correct.

Being able to ignore one of the measurements and just let CC3+ handle it is a good and time-saving thing, but it does mean the map must meet the expectations.

CC3+ always does a split install. The actual program itself is always installed to the C-drive, but it is extremely tiny (less than 100MB with absolutely everything installed), the rest goes to the location you chose for your data directory in the CC3+ installer (Which I presume is e:\ something in your case), which is the bulk of the install (art, configuration, templates, maps, drawing tools, symbol catalogs, and all the rest)

Any add-ons installed after that will never ask for location, but just go to the appropriate directory of the two. Components needed by the program itself (mostly things like .dll files) will be added to the folder on C, but any content will be added to the data directory in your chosen location.

Not as far as I know.

But maybe you can work around it. One way I can think of is to combine all the individual polys into one massive one using the CONTOURSM command. This will create a single polygon that matches the complete outline of the existing ones, and you now have a single poly to use the area command on.

I don't remember the screens in the installer for the Annual 2023 off the top of my head, but at least some of our products have a screen with a checkbox that enable you to do an "artwork only" install (for use without CC3+). I don't remember if the 2023 annual had this, but if it does, make sure to NOT enable that option during install, or it will only install the artwork for use with other software, and not the CC3+ components. Try rerunning the installer and see if this is the case.