That what you have posted seems pretty normal startup flow. Seems you have skipped just the most important part, that's carrying information of what's going wrong, if any. 🤔
By the way, it's always better use of control script to install and start the daemon. It gets automatically installed when you install cresponding package (deb or rpm - what is matching your distribution). The debian package in your case.
... The last problem is I can't get the daemon to stay up and running when the ssh connection is closed or the server is restarted. ...
Probably you miss understanding that Dropbox application is user mode application! The same like a office package or messaging service (i.e. like any other user program). When a program lose the session (i.e. particular user, running the application, logs out or the system shuts down) execution terminates at that moment. That's exactly what happens when your "ssh connection is closed or the server is restarted". Dropbox doesn't support daemon's system mode work (I have no idea why), unfortunately. That's not a supported option currently. Of course you can make your own control scripts and use them to launch the Dropbox application in a persistent session. You can take an idea from other system services scripts, like such for MySQL, Apache, etc. (which could run both in user or system mode)
Hope this clarify matter.
Add: If you want, could give a vote to idea I just shared.