Beginning with Taproot? Hmm... Something about this feels scary to me.
Your mistrust is misguided.
So, they are no longer making "signed" installers?
The releases are still signed with the release GPG key, what is lacking is the Windows specific binary signatures which have to be made by a paid certificate by one of several authorities Microsoft ...
You'll want to set the option -datadir=<path-to-your-drive> either when starting bitcoind, or in your bitcoin.conf file. If you add it to bitcoin.conf, you'll need to restart your node for the change to take effect.
If you want a definitive answer, you'll need to ask him I'm afraid.
My best guess is that Windows development was the thing he was most familiar with (or even only familiar with). The coding style was also similar to one commonly used in the 90's by Windows developers.
As Pieter pointed out, it sounds like your Bitcoin Core is not shutting down cleanly when you turn off your computer. This could happen for example if the shutdown process does not wait for Bitcoin Core to shut down cleanly before killing it, or if the computer is just powered off immediately.
Bitcoin Core caches progress to the chainstate¹. The chainstate ...
What other measures can a new, non-power user take in order to protect from this type of significant theft, within reason?
For money stored long term, move the coins to a hardware wallet or some form of offline wallet (cold storage).
Use a transaction (rather than importing keys or using an existing seed-phrase) to move the money to a wallet with fresh keys ...
Unfortunately, good security isn't always easy.
In this case, your worry is not unjustified, and it is why most security-conscious users will recommend never having privkeys touch an online device. This is, at minimum, required to mitigate against the sort of software-based attacks you've outline above. IF you have an online computer that holds privkeys and ...