If you're like me, a long time Mac user with a lot of time spent in Windows for work, I think it's really pain free to switch.

I chose Debian -- the distro for boring people. Supposedly, it's the best for stability and compatibility, not the best for cutting edge applications and perhaps slow to get some drivers and what not. Often people suggest alternatives like Mint as user friendly. However, I haven't had a single problem with Debian in terms of compatibility or usability.

For the "Desktop Environment" (DE) -- that which impacts the most whether the system feels more or less like MacOS -- I use the bundled KDE Plasma without modifications. Like on Windows, the most used keyboard shortcuts, by default use Ctrl instead of CMD. If you're at all used to Windows it will take you no time to adjust -- otherwise it may take some rewiring of the brain or rebinding keys. The stock file manager in KDE is nowhere as nice as Finder, but also trivial to adapt to. Overall, KDE Plasma does not really mimic the feel of MacOS at all, but I consider that a pro -- it means that I don't end up frustrated assuming something will working the same way when it doesn't.

I have never been big on using the official App Store on MacOS, but if you are, that's going to be an adjustment. Each system comes with something similar to the App Store, but they generally don't come with the same range of apps (e.g. Debian/KDE has an app called Discover which has a really narrow range of apps). However, as you're stated goal is to break free from big tech, getting to know the different ways of installing apps will be a rewarding experience (and rather straight forward, most of the time).

Speaking about apps, I think one of the pains you should prepare yourself for if you decide to stick mostly with apps that are "Free Open-Source Software" (FOSS), the degree of polish -- particularly in terms of investment in GUI/UX -- will generally be considerably lower than many paid apps you might be used to, particularly premium Apple apps (e.g. Final Cut).

As for hardware, I don't really have any valuable pointers. I think losing out on the great synergies between Apple's excellently built hardware and very optimized software is a big trade off. But depending on what you're gunning for, you will have a lot more options and potentially at a better price/performance point.