Great job!
A+ for having the fdroid install.
Have you looked at sandstorm.io for self hosting support?
I like your landing page. It's fairly clear the values your offering but I'd expand on what clients you are going to end up using after migrating etc.
"""It seamlessly integrates with Android so you won't even notice you are using it."""
Might become
"""It seamlessly integrates with the current Android calendar/phone/contacts applications so you won't even notice you are using it."""
Nicely done. I think it definitely is an area that needs this or something very close to it.