I've been using fastmail for the past 3+ years in an effort to de-google my life. It's been excellent, and I haven't had any issues with emails I've sent being classed as spam.
+1 Fastmail, though make sure you use a somewhat standard TLD if you go for you own domain (I had a .xyz one that turned out to be marked as spam too often, and switched to .nl later)
By the way, it is possible to sync the calendar and contacts with your Android phone using davx5 (available for free on F-Droid)
Fastmail makes an excellent email client, but there are significant privacy concerns that have not been adequately addressed in many people's eyes.
Namely, that Australia (where Fastmail is based) passed laws that require all Australian companies to give any/all data on their users to the Australian government, and are not allowed to publicly disclose what is given.
Not that Google is any better.
If you want a privacy-focused email that "just works" consider Protonmail or Tutanota. Alternatively, if you're feeling bold, you can self-host your own email like I do, but I wouldn't recommend it unless you're in it for the fun of it!
I don't think I'd ever noticed this. Flipping between the system font option and Proxima Nova, there's not a huge difference (on a Mac). I do find it subtly easier to read however, so would agree that attention to detail is neat.
