If you are already using gimp for photo editing, you won't have an issue there. I had to do the switch from Lightroom & Photoshop to Darktable & gimp. There was a learning curve for myself, since I had to re-teach myself some shortcuts, and get used to different interfaces for the same/similar tasks. If you're already working with gimp, then you should be golden.
I haven't used Blender myself, but have heard good things about it.
FreeCAD is certainly doable, but I found it a bit overwhelming for what I needed it for. I didn't like the idea of using SketchUp for Web - I try to avoid web based apps whenever possible, but it was much closer to the level of simplicity I was looking for.
If you are interested at all in light video editing, I recommend checking out "kdenlive". It's worked great for me for short clips, or random webm's I've needed to make of various things. Being video editing software, there is obviously a curve to that as well, but after looking at one or two YouTube videos, I was able to get by with the bare essentials. If you're looking to stretch into other creative areas, it's worth checking out. It doesn't sound like much, based on the name alone, but it's surprisingly good, IMO.
As far as distribution recommendations, I would immediately suggest Fedora Design Suite. It's a great mixture of stability and regular updates. The interface isn't too difficult to get used to (although I would suggest turning off "Hot corner" if you are going to be doing a lot of editing. I found myself accidentally turning that on. There's a simple on/off switch in settings for it.) The interface for Fedora is very well thought out, and, although it is distinct from Windows, everything is in a logical place. I also didn't have any issues with Wifi or Bluetooth out of the box, which was a really nice perk.
On a house-keeping note: I tend to use the following command to update roughly once per week
sudo dnf upgrade-minimal && sudo dnf update
upgrade-minimal ensures that you are getting bug fixes and security updates, without introducing issues that might interfere with a project you might be in the middle of. I try to ensure everything is fully up to date every month or so by dropping the -minimal part, but I like the flexibility of not having to worry about it until after I'm done with whatever task/project I'm in the middle of. I hated when Windows, or some other program, would twist my arm into an update, and break something in the process.
I was really nervous that I was going to be taken away from the content I was editing in order to troubleshoot some random problem with Linux - that's the perception that I had of it for years. But with Fedora, I haven't had to worry about that at all. I can't speak for other distros in that regard, I'm sure a lot of them are great. I was just really blown away with how well Fedora worked for my use case.