What are the principal technical skills a bitcoin lover needs to have if I want to buy a large amount of Bitcoin and hold it for long-term purposes?
If you don't have enough knowledge then you have to keep various precautions,
1st one is you need "don't talk with any unknown person via social media" most of the extraneous could be an imposter.
If you want to hold a vast amount of bitcoin then 2nd one is you need to buy a hardware wallet, generate seeds and address by using HW wallet and print that on a piece of paper or metal, make some copy, and keep your copy in any fireproof & waterproof locker.
you can use any watch-only wallet and import the btc address as watch only. It could be the safest way to hold your coin securely.