I did not invest before because I was afraid of not being tech savvy enough to manage a wallet. I don't trust Ledger, for example.
I wouldn't trust Ledger either, but mainly because they exposed their customer's personal data, lyed about the seed can't be pulled out of the hardware and their firmware is closed-source and thus opaque.
But there are excellent alternatives besides Ledger hardware crap: Foundation Devices Passport, Trezor Safe 3, BitBox02 to name my personal favorites. You have good choices, no need for Ledger crap.
A guy in my class at uni manages at least 10 BTC, or more. He's secretive about it.
Apparently not secretive enough or how do you know that he manages at least 10
BTC? Did he brag about it or is it just your own wild guess?
Simply don't talk about how much crypto you have or you want to invest in. No need to disclose such sensitive and potentially dangerous details. Why risk getting in trouble because of that?
This will require a 20k bank transfer which will automatically flag me to the authorities. They will know I'm into crypto and I think it is a matter of time before I have to declare the holdings on my tax sheet.
You don't need to invest such a sum in one transaction if that raises flags at your bank(s). Don't rely on advise of others because others rarely act only in your interest but rather in most cases for their own benefit. You should understand the investments and their risks you are about to make.
Don't try to evade proper taxation of your crypto investments, it's usually not worth the trouble. You might be lucky, but if not, you're gonna be in deepest shit pretty quick (of course depending on in which country you live, but usually everywhere tax evasion isn't a small and neglectable misdemeanor).
For the amount you plan to invest I would strongly suggest to protect your wallet secrets with a hardware wallet. Proper usage of a hardware wallet, learn the basics first, shields your stash from a potentially insecure computer environment. Don't do your daily internet shit on the same device that you use to communicate with your (hardware) wallet. Try to separate crypto stuff from your daily internet stuff.
Don't become reckless, there's usually no "get rich quick" for all of us.