Technical skills ?
I am really not sure if that's needed for holding.
If you do know your basics you are good to go and you learn along the way, it's not a hard task to just hold but the hard task is to be *patient*. I would rather give more credit to the mental skills and the decision making.
-You have to give prime importance to *security*, cyber crimes are more pronounced in this industry for sure. Also looking for a good hardware wallet will be the first thing that you should do. Research, Invest in a good one and do not keep such huge amount of Bitcoins in any Online/offline wallet.
Best of luck with your journey.
~

If you have not much of computer skills and want to buy/hold bigger amount of coins, I'd suggest you start with buying a hardware wallet, which will help you generate safely (new) seed for your address(es).
The only next step is to write that seed onto one or more pieces of paper and keep them safely offline (for the case the hardware wallet malfunctions). And that's basically all imho.
The coins you bought you'll have to withdraw to one of the addresses you own (since only then they're really your), but if you have difficulties you can always ask on this forum.

Not quite technical skills, but you should;
• Be privacy conscious and learn how to use a P2P platform for purchase or buy through OTC trades,
• Understand the basics of how a wallet works, setting it up, how to send and generate an address, lock an input etc,
• How to use an airgapped device, if you do not own a hardware wallet,
• Possible how to mix inputs to blur the trail of a transaction,
• How to browse safely to avoid falling for scam attempts.
• Also, how to safely store back up seed phrases for a long period of time.

I'm not sure what you mean by technical skills, but at least some basic knowledge of computers. Then you need to understand how to transfer bitcoin or withdraw, or what is your bitcoin address, private keys and then storage, which is usually a hardware wallet in case you want to buy large amount. Usually a hardware wallet is a good way to store your bitcoin specially if you are planning to just hold on it for a long time.

What you need to do is to learn first the risk when you buy bitcoin in certain time since there are instance that we are prone for market crash, hacking or anything danger which can cause our bitcoin lose on our hands so invest on knowledge first before buying a huge sum of bitcoins. Also I know there are few people use exchanges as their placed to hold their bitcoins and you shouldn't do this since there are instance that exchange got hack so its so risky if you decide to use this as your holding destination so better invest on hardware wallets as suggested for better security.

If you can not buy hardware wallets, you can use Electrum or Wasabi wallet
Recommended wallets

Exchanges won't support to recover your coins if you send it to address of altcoin, not Bitcoin. If they give you support to recover it, they charge you expensive support fee.

Save them off line

If your going to become your own bank, and will be responsible for your money, without any third party stepping in to save you if you make a mistake. Your probably going to want to learn about securing your Bitcoin, but also having good security practices in general. Depending on your usage, you might want to learn general computer security if you intend on running a hot wallet or just learning about common Bitcoin security if you intend on running your wallet offline.

If you are running a hot wallet, then I suggest securing your system from the bottom right to the top. Think securing your browser, changing your browsing habits so that you aren't putting your system at increased risk. For example, don't download software which you don't trust the vendor that is distributing it. Physically isolate or virtually compartmentalise your system if possible. There's no real one place for learning this sort of stuff so you'll have to be prepared to search it up on your own. Ubuntu, or Linux tutorials are generally pretty good at teaching you how a computer functions, and the things that you can do to enhance the security of your computer.

For example, Linux teaches you about chmod; basically access, and writing permissions which many Windows users don't even think about. Then, you could potentially take some courses in Cisco, and CompTia if you really want to brush up on your skills. Though, most of these skills can be learned from free resources.

Emotional control is very important for you to master. It's useless the capital you spend is big but emotional problems can't be restrained, it's useless. So it's good to control your emotions when dealing with the market. Strategy in trading is also important so that you are not confused and swayed by the market. The strategy must also be applied consistently in order to minimize changing strategies that can make you sway.

In my opinion, some important skills would be to know how to safely access your keys to your coins/assets from the Blockchain wallet on a secured device, and safely store the keys.    I actually prefer not to have single key for all of my coins/money just incase it's found by a thief or something and the whole coins is stolen using the single keys. You could split the money into multiple parts and have different keys for them which you can engraved on a multiple object like metals and buried/stored them somewhere you can easily remember and access when you need to.

I don't know about you, what's your interest, if it's the inner workings of bitcoin then the technical skill that you want to have should be coding and networking skills. They can help you understand the movements of the network and you can understand how the code of bitcoin works. Probably some willingness to learn could help too because there's a lot to learn in this platform and bitcoin and cryptocurrency itself.