My issue is, I'm not sure if there's an edition of live windows that can be used (linux seems too dependent on its dependencies to be useful to me - too much reliance on running random scripts from the internet).
Why do you think that linux requires to run 'random scripts from the internet' ?
You don't have to run any scripts at all. And obviously also shouldn't without inspecting the code first.
For security reasons, i would discourage you from choosing windows over linux.
I don't have the time to read the source code for bitcoin core, libssl-dev and the other requirements needed
Security should be high since the device/disk won't touch the internet, people who moan at windows not being secure is generally because they like how they can download loads of random stuff to it. I don't like that idea of downloading random addons (and I don't think I've downloaded very much to this machine for example that can actually run)...
My computer shuts off if an "untrusted" program uses more than a certain amoount of memory, data or cpu power (only things that are trusted are things like bitcoin core, litecoin core and electrum - my laptop dies if I stay on the forum for too long because it fills up the ram beyond the trusted limit (not just because I don't forget to plug it in
))...
Is it safe to assume, once I've sent an amount of coins there and none of them leave and my seeds have been taken completely offline and just stored in a notebook somewhere that my coins are safe for any new coins - I'd use my phone but that seems to have a limit of 5 keys?
If your seed has been generated properly (i.e. trough trustworthy (verified) wallet or through good RNG) offline AND the computer which has the seed stored in a text-file does NEVER touch the internet, it is pretty safe to assume that it is secured.
Without being able to connect to the internet, a potential malware couldn't connect to send the seed to the attacker.
But you should still use a non-digital backup of your seed. Your system/hard drive might break. Or a lightning strike could destroy your hardware.
It is always good to have a non-digital backup for such cases.
I'll just claim it back on the insurance from the lightning strike
.
Although my non-digital copy of the seed might be frazzled, ash or molten by this point too?