You can do Symdefs to Sheets from the Symbols menu. That turns all the symbols into sheets in the same drawing, making it easier to edit multiple symbols at once.

You don't need any of the CC3 stuff. A lot of the products will have installers for both CC3 and CC3+, so make sure you get the CC3+ installer for all of those, they should be labeled.

There's no specific order of installation, but you should always install the latest update at the end after installing everything else. This is because it doesn't just update the core program to the listed version, but it also updates all the add-ons at the same time.

Use the :CC2EDIT: command on the lights directly in the map (visualized by a cross in the light's color)

What you are experiencing here is an issue nicknamed 'Transparancy Acne (TA)'.

What happens is that as CC3+ stacks sheets on top of each other to generate the final drawing, it needs a way to figure out the Edges of the entities on the sheet just added, so it can apply edge effects. It does this by looking at the difference of the stack of sheets up to an including the prior sheet with the stack of sheets up to and including the current, and then computes the differences.

Unfortunately, when the new sheet have parts that are new, but identical (like you are using the same parchment here, although one is a bit modified, it is still the same parchment) the effects will see those parts (can be as small as a pixel) as holes with edges around and thus apply edge effects.

One way of handling this is to simply stick a sheet with a copy of your entity in between the two sheets with the parchment, and apply the same edge fade to it (maybe even a bit more). Another option which may work in your case is to change the color of your custom fill a little bit, that might be enough to avoid the issue.

Unrelated to this, you'll want to make sure to use relative paths for your fills styles, will save you issues in the future.

More like up early, caught it before going to work :)

For line styles, look at this: