I am wondering a bit if it's even a good idea to get a monitor that doubles as a TV
You might be thinking about it backwards; It might be better to get a TV that doubles as a monitor.
If you are going to be sitting very close, like it's at a desk, then that 43" screen is going to be like having 4 1080p monitors without the borders. It will be extremely useful for showing tons of content open all at once. When you're using a screen in this way then the features like Dolby Vision and 24 Hz aren't even being used in the first place. HDR isn't that nice for regular PC use either so most people turn it on only when they watch shows or games.
If you are going to be sitting further back and that 43" screen will be used more like a single display for lots of fullscreen stuff then a TV is probably the better choice. In that use case you're probably going to be spending more time watching shows and movies than having dozens of windows open for productivity tasks. (It's not nice to work like that from a couch).
are they a big deal when it comes to viewing experience? Say when watching Blu Rays or the occasional stream.
Dolby Vision is not as important as having just any HDR support at all. This screen does support HDR10 and it will probably do a pretty good job at it too. Dolby Vision is just a slightly nicer variant of HDR that handles the tone-mapping a little better and closer to the original intent of the content creator.
24Hz is not really that important for monitors. Since many TV panels are run at 60Hz or 120Hz it means TVs need a specific feature to actually change the refresh rate of the panel to match the content at 24Hz. On the PC you can just change your resolution and get 24 Hz by setting up that display mode manually.
However, 24 divides into 120 Hz perfectly so running the Aorus FV43U at 120Hz would mean you get both the perfect 24 Hz and 60 Hz playback without having to change the display mode.
I would say these two features don't really matter if you fall in to the PC use-case I described above. Dolby Vision matters just a little if you're expecting to use the screen as a TV more often and actually play Dolby Vision content too. (i.e. Netflix and new Blu-Rays)