JoePreiser has a good description of your choices.
In my case I run the Server app on my main iMac. It’s sole purpose is to run WEBDav for my sync of both DEVONThink and Omnifocus as I am very cloud adverse and do have lots of very sensitive information in both software packages. I put all my databases onto the DAV folder and sync to there. I have separated my databases so that the ones I wnat on my mobile devices are fairly small and the ones I only need access to on the macs are large.
I pull the full contents down into the mobile devices rather than waiting to pull the info down as I access it.
I know things would be a lot faster if I had a separate Mac to run the server app but all my other macs are in use and this works. Occasionally it gets slow but livable.
It is true that when I am out and about I cannot sync my devices but that isnt an issue for me as I can get back to my home base and sync easily. I could set it up so that my WEBDav is visible to theoutside network to give me mobile sync but I haven;'t botherd to yet as I don’t need it.