+1 on almost everything you wrote. I also moved from Gmail to Fastmail in almost exactly the same way some months ago. I agree completely to the plusses and minuses you mention.

I would like to add one minus though. Any good old smiley like ":)" in emails gets replaced by a yellow smiley face icon. I hate to see yellow smiley faces where someone wrote colon end parenthesis. It's all done client-side though, so noone else has to see it. Have been in contact with FM tech support and they seem to be uninterested in adding a checkbox to turn this nuisance off. Otherwise an excellent, excellent service.