I use Fastmail for email, contacts, calendar, reminders, and notes. I have been an extremely happy customer for several years and I am happy to promote them. I don't think I've ever used another web-based service that has such a high "usefulness/power : annoyance : money spent" ratio.

I use paid Seafile hosting for file sync. I haven't tried Syncthing, but the Seafile clients all seem to work very smoothly.