which is primarily handling word documents, viewing PDFs, watching evidence videos, and online research. But my concern is that some of the more commonly used video types might have trouble on Linux, or that some of the word document templates I use in Windows might have compatibility issues.

PDFs, at least static ones, are no issue, you can download Okular to trial-run that. Neither are video codecs: On windows you can give mpv or vlc a spin, both play practically everything under the sun^1^

MS Office is the actually iffy point. If it's just your own templates that's not much of an issue, you can migrate them in one fell swoop (and re-do them while at it probably making them better), but if you have to regularly deal with templates or worse advanced Excel stuff produced by others then that's going to be a never-ending saga. As with video, you can trial-run that stuff by installing LibreOffice on windows. Dunno whether that's an option for lawyers but you could also use the online version of MS Office.

What else might I need to know to use Linux comfortably from the get go? Is it going to take a lot of time and effort to get Linux running how I need it to?

It also runs in a VM. You can give different distros a spin without committing anything but a bit of bandwidth and disk space. Next step: Boot from USB to go over hardware support.

^1^ except variable bitrate realmedia, the only thing that ever seems to have been encoded with it is the ArsDigita lecture series, now re-coded on youtube no issue. The reaction on IRC when I asked about that more than 10 years ago was "It's always those lectures, isn't it" and "No". Side note in case you have some time to kill