Okay so I am typing as someone who has helped local businesses set up computer systems. Nothing big just one or two person operations. Getting them computers, downloading their software, and making sure they understand how to keep up to date.
I would recommend you use what you are comfortable with at first. Use Windows, get your business in a comfortable position to experiment. And then I would say try Linux out.
I imagine you will need to keep up to date with invoices and the such and you will need to figure out what software you are going to use that. You could always just be basic and use excel sheets but most businesses are using Quick-books or something similar. And a lot of invoicing software does not work on Linux. I would say invoice-ninja is probably the most popular invoicing software on Linux so that would probably get you the best support. This is usually the point people tell me they will stick with windows.
But if you are able to get past that and maybe learn one of those invoicing software applications then I would say you would have next to 0 issues. As you are in a business environment pick something reliable. Debian, Ubuntu LTS, or RHEL. I would test them all in a vm and see what you like best.
Now word documents may cause issues. Maybe. I find libre office works for me 95% of the time. But I don’t do anything very fancy with it. I write essays and maybe every now and then I will include a graph. I would test libre office on windows and see how that works for you. Only office is also an option but I have 0 experience with it.
Also I find that linux is seriously lacking in ways to manage pdfs. At this point I use my browsers built in pdf reader more than any sort of linux app. Digital signing has always been a pain in the ass and the pdf reader I have the best luck out of is Zathura which is a cli application which is definitely not new-user friendly. But this isn’t really an issue it’s just me nitpicking. You can manage pdfs on linux just as well as windows it just may not be as user friendly some times.
You mentioned you are worried about some video formats not working on linux. May I ask what sort of video formats those are. I find vlc or mpv to have great support for most if not all video formats.
My recommendation would be to use linux. I love it. But this is a new business. Use what works for you as much as possible. Get to the point where you have the funds and free time to experiment and try linux. Poke around with some open source apps in windows and see how they work. Invoice-Ninja and libre office both have windows versions.
I wish you luck with your endeavors and I hope my comment has helped somewhat
edit: spelling and punctuation
https://terminus-font.sourceforge.net/ this has been my favorite for a while. It keeps the retro sort of look while still being actually ledgible