For sharing, yes, it is completely fine. The only things that matters when sharing the file is that the recipient have the actual art files on disk. You can make as many fills as you want inside the map without that being a problem, sharing issues only becomes an issue if you manipulate the png's on disk (such as making copies of them). As long as you can see inside that fill style dialog that both versions point to the same png files, then everything is fine.

The technique Ralf showed here unfortunately only works with bitmap fills. This covers most maps, but some maps, especially maps using line-work (like the landform maps) use different techniques for the fills.

It gets a bit more complicated to scale these. I am pretty sure Ralf showed that off in a video at some time too, but I don't remember which off the top of my head. I'll see if I can find a link for a video or something else, unless someone bets me to it.

If you try with for example the Mike Schley overland style, you'll find that this trick works the way Ralf showed it if you use it on a bitmap-filled polygon, like farmland for example.

edit: Ralf demonstrating editing hatch styles in here: https://www.youtube.com/live/-zZGWKT2pN4?si=LOm5YLc6CtJAds-j&t=1187

If you look at the prompt while using a mirrored polygon drawing tool, you'll notice that it offers you to hold down the control key to create smooth nodes. This allow you to create a plan that has both curves and straights in the same poly.

Sounds like an interesting idea. While I have no idea if something like this will be made for CC4 or not, you can already today get access to all the data needed, so that should be able to be done with an add-on, meaning even if it isn't put into CC4 by default, it should be possible to write for anyone with a bit of programming experience and put in without PF having to add anything to pave the way.

Maybe not exactly the way you describe, but you can add large amount of text to your map using map notes. These don't display in-map, but in a separate window, but you can make hotspots to click to show the note you want, and each map note can have up to 8000 characters. Not quite unlimited, but room for quite a bit of text.

I do this frequently for atlas maps, for example, try downloading and opening the Southern Scar map from the atlas, and hit the Description link in the sidebar, and you'll see a description of the map appear. This is a standard hotspot that can be placed anywhere in a map.

Some more information in this blog article: