+1 for the Pomodoro technique here. I use tomato timer (https://tomato-timer.com/) to make sure I stick to it, and I find that the 30 minute stretches are just right.
I use Thunderbird for emails, keeping current jobs in my inbox and shifting them to separate client folders when they're done - you can tag emails with different colours if you like, but I've never found that helpful.
What I do find essential is a simple Excel spreadsheet showing the jobs I'm working on, the word count and when they're due. I keep that open pretty much constantly, so that I know what I should be concentrating on at any given time, and also to give me a simple overview of my availability for the future.
As for backups, these are a must. I use another drive too, like Eleonora. When I first started out, I didn't do this kind of backup, but it only took one dead laptop and a consequently lost client to teach me that particular lesson!
