Evolution, Thunderbird and KMail, depending on the system. Though I've had only trouble with Thunderbird and gpg signing with a yubikey. The others just work.
I get a summary once a week of all the updates. I then check the release notes and if nothing needs any changes just run the ansible playbook that updates to those releases. I don't want to get up and first thing in the morning read alert emails because an update failed over night, so i sit down for 10 minutes once a week.
Contabo is really cheap and has a few datacenters around the world. That low price comes at a cost though, their uptime is not as good as that of other providers. Expect about 3 outages a year, lasting about half an hour, maybe a day in extreme cases.
Didn't really hop much, started with Windows, went on to OSX, got annoyed at it and ran Arch in a VM until I was comfortable with it, then went bare-metal with it.
Happy Arch user for some years now, though recently I'm using Fedora for work and I really like it. It's not a good fit for some machines I'm running which need a lot of customisations to run properly.
I usually use bash/python/perl if I can be sure that it will be available on all systems I intend to run the scripts. A notable exception for this would be alpine based containers, there it's nearly exclusively #!/bin/sh.
Depending on the complexity I will either have a git repository for all random scripts I need and not test them, or a single repo per script with Integrationtests.
Depends, if they are specific to my setup, no, otherwise the git repository is public on my git server.
Usually no, because the servers are not always under my direct control, so the scripts that are on servers are specific to that server/the server fleet.
Regarding your last question in the list: You do you, I personally don't, partly because of my previous point. A lot of servers are "cattle" provisioned and destroyed on a whim. I would have to sync those modifications to all machines to effectively use them, which is not always possible. So I also don't do this on any personal devices, because I don't want to build muscle memory that doesn't apply everywhere.
I wrote a small program for the arduino nano 2 years ago, it isn't that fancy, a quickly hacked together led flash animation, but the Makefile works. You really just have to install the dependencies and adapt it for your project and it should work.
If someone comes to me I'm more than happy to answer questions and help, but I won't bring it up. People don't like being told that their tool of choice is "bad" "not optimal" or anything like that. Even if it's only their choice because they grew up with it or don't want to learn anything new. And they still need to learn if it's more than browsing the web.
Also I really don't want to be the one they come running to once something doesn't work the way they expected - or not at all. I don't have the time nor the inclination to be tech support for my family and half of my friends.
Cries in 1080 ti