That has little to no effect.

What usually causes the problem is if you have loads of House entities rather than symbols, because they are built from filled polygons and dramatically increase the node count.

You can work on a district at a time and then move a completed district to a layer of it's own and hide it until you need it later to check on how things look overall, or for rendering.

Use List in the Info menu to find out how many nodes you have in that large landmass. It's the node count that really slows CC3 down. over 10,000 is where it starts to get slow, while 30,000 is nearly impossible to work with. But do you really need that many? In most cases, not really.

If you can get away with it without losing something important, use SIMPLIFY to get rid of unnecessary nodes. Even if you use a very small factor with SIMPLIFY, it will still get rid of any nodes that are right on top of each other and not really doing much because they are too close to make any difference.

Fractalise is a high risk tool to use. If you use it too many times all you end up doing is making the coastline frilly and CC3 slow, neither of which are good things. I don't recommend fractalising anything large more than twice with the default settings and definitely no more than 3 times. You also have to consider that however many nodes you end up with in the coastline you will double that if you then trace the coastline with all your terrain fills.

If you want to be able to edit and trace your coastline, use a colour key for the central ocean instead of multipolying the two parts. A multipoly can't be traced, edited, or fractalised.

This is a bit different to entire toolbars vanishing, so it might be worth re-contacting Tech Support before you reinstall if it comes to that.

Here is a suggestion that might help achieve the look that you want.

how about making the sky fill a solid blue, and adding the cloudy bits as fuzzy edged symbols? If the cloud symbols are mostly transparent you can build up thicker layers of cloud by overlapping or placing them on top of one another.

In the bottom map you have a slight issue with the text being a bit invisible against the trees. If you add a white Outer Glow to the TEXT sheet it will wipe out the trees just around the letters so you can read them better.

(The text sheet will need to be under the parchment sheet, so that the white simply disappears)