Which secure BTC Wallet do you recommend for me to hold?
You can use the best wallet in the world and still lose your coins if you don't protect seed words correctly, but best wallet should be with Open Source code.
There are plenty of option to choose depending of what coins you want to hold.
Best option for newbies is using open source hardware wallet with additional passphrase for better security.
I heard about 25th words of 100 characters and multi sign.
Don't experiment and don't make things to complicated.
Multisig setup should only be used by experts or advanced users, and it is increasing transaction fees.
It is even easier to lose your coins if you don't do multisig correctly.
I thought about Tails live USB which has electrum in wallet.
This is solid option, but it's not for newbies.