Due Diligence Self Custody Practices

Looking to finally setting up a decent due diligence practice for my self custody btc holdings, this is quite challenging for me as a non tech guy and it's making me even more paranoic than usual. It's also a bit fun too to be delving in this cryptographic world

What I want to achieve:

1 - Generating a solid 24 words seed + passphrase

Plan is to use Ian Coleman or Bitcoin Core: but having trouble on being 100% sure I'm on the legitimate Ian Coleman html or Bitcoin Core Software.

I'm learning about this PGP and signatures checking to make sure I have the legit stuff. This is quite a challenge. I'm on windows and most people teaching this stuff are either on mac or Linux.
My Kleopatra is not recognizing the Ian Coleman Pubkey (Getting this message when importing pubkey: "Total number processed: 0 Imported: 0") and I didn't find the Bitcoin Core pubkey to download too.

Is it essential to check this signatures stuff and to learn to use Kleopatra/PGP software indeed? How vulnerable am I by just double checking the URL of the software's I'm getting?

And besides that, is it already sufficient to just turn off internet/Bluetooth on my main desktop to generate the keys? From what I understand, best way would be to get a basic rasperry py 0 and generate it airgapped in a hardware that was never and will never be online. Am I being overly paranoid here or this is solid practice?

2 - Define how to store the seed + passphare: honestly this is very difficult. From what I understand, it is better to segregate seed and passphrase, but it's not like I have bunch of places of my own to hide different parts of it. I'm able to store one seed and one passphrase safely, but then it's only 1 copy of each and if 1 gets compromised I'm fucked. In short, what are some good practices to store seed + passpharse for some1 who doesn't have multiple solid locations to store it?

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This is it, it's worth saying that today my self custody practice is very vulnerable and any improvement is very valuable. This makes me think I'm losing to much time trying to understand and make a very solid setup but while doing that, I'm extending my exposure time in this vulnerable setup. Not entirely sure if I should just improve it as fast as I can to decently better set up or if I should do it slowly but improve to the best practice I can at the end of it.

Any readings/websites/youtube channels that are solid for understanding and getting better at this aspect of the game is highly appreciated.

Thanks and blessings for you all