The Moneydance solution embraces 5 operating systems; Windows, MacOS, Linux, IOS and Android.
The problem with most of the cloud storage solutions is that they do not support all 5 systems, thus limiting their usefulness from a Moneydance perspective.
The Dropbox 3 connection limit for their free account need not be a problem. The Mobile devices used the Dropbox API and thus do not contribute to this limit.
Desktop/notebook type devices only use one of the connection licenses if you use the Dropbox Client along with the Dropbox folder syncing solution. If on any of these devices you remove the Dropbox client and change the syncing solution to Dropbox Connection then that device will no longer use one of the client connection licenses and thus not contribute to the limit..
There is no issue in mixing Dropbox Folder and Dropbox Connection in the one solution
Fellow user on a Mac. I'm syncing through a shared folder that's on my NAS. I'm syncing between an iMac and MacBook and it seems to work well. I know many of the public cloud services (Dropbox, Google Drive, etc.) have syncing clients to sync a given folder on your computer to the cloud service. Maybe try that approach?