I did exactly what you did initially to test out this product, by hosting a web version of it on my home server. It was great but the experience on mobile was not perfect.

A couple of weeks later, I purchased the pro license and I now use SiYuan on all my devices including my mobile devices and got them syncing successfully without issues via a WebDav server. It currently runs on my VPS but I do not see why it won't run smoothly on a local Ra Pi machine. Your setup should work fine, but not having access to sync outside home sounds messy to me. Also the app gets quite noisy when the syncing fails, which I look at as a good thing. Note that syncing doesn't happen instantly on updating any of your notes, but it happens on a "every 30 seconds, and on opening/closing app" basis.

You can still make your setup work, and you'll be able to update notes and add assets etc as you need. But you need to remember to sync your notes as soon as you get back that access, or else you might run into annoying conflicts.