1 + 2:
There’s not much involved in burning an ISO to a flash drive, booting from it, and installing typically. It is different in booting from one on a Mac. If you have an M-series Mac, you will be restricted mainly to anything with the experimental Asahi Linux kernel. If you have an Intel-based Mac, you should generally be good to go. Whenever booting a Linux installer, you’ll generally be able to check out the system before installing. It’s a good time to check things like backlight brightness and wireless capabilities are working out of the box on your distro of choice.
Accessing the boot menu on a Mac
3:
OpenSUSE Tumbleweed and Fedora are generally good picks. I recommend going for KDE unless you have a strong preference for how GNOME works. As good as the distros are, I generally recommend staying away from distros like Linux Mint (for now) as their implementation of the newer display system called Wayland is not yet complete for Cinnamon. Desktops like KDE and GNOME have functional implementations and will overall provide a solid experience.
4:
You’ll see mixed opinions all over the place with this. Personally, I do sit in the GrapheneOS camp at this point. If you don’t want to purchase a secondhand Google phone, I’d wait and see for the partnered device that GrapheneOS devs are in works with a currently undisclosed manufacturer on.
I’ll repeat the core points the GrapheneOS devs drone on about other Android OSP distributions, but without the hyperbole the devs constantly put in. Yes, e/OS does generally have security problems, some of which stem from the use of microG, and how microG just has to function on the device. It is a trade-off in security for some privacy gained. If you really don’t need anything of Google Play Services at all, you could always go for straight LineageOS without any Google services package installed at that point.
5:
By all means, older laptops can definitely still be functional for lighter or alternative tasks. Even if it’s not a good workstation anymore, could be fun to experiment with. Older phones (especially Android devices) really do have a set lifespan that I’d recommend to stop using them as daily drivers. When the manufacturers stop supporting them, they can be horrifically vulnerable devices as exploits are found over time. You might still get use out of it though without using its networking capabilities. It likely still has functional storage, screen, cameras, etc. If you’re lucky, you might be able to play around with straight Linux projects like PostmarketOS.
For new stuff, Linux-centric vendors can be nice (though a lot of them seem to just rebadge Clevo laptops with a decent markup) as a guarantee of good hardware support. Most business laptops make for good Linux laptops. I personally bought a Framework 13 a few years back and that’s my primary laptop. Though if you want to stay away from United States-based projects, your initial choices are probably a good fit. Additionally, you might lean more toward OpenSUSE than Fedora as well in the same principle.
In addition to the other reply on the fundamentals of why not in general, maybe we don’t recommend daily driving one of DHH’s pet projects.
If anyone is out of the loop of who DHH is, tons of people have covered the topic but I think Niccolò Venerandi has quite comprehensive and digestible coverage. If anyone cares to read or watch Nicco’s coverage.