Using only wallets that connect you to blockchain is safest
Using wallets that require email or private key is not best at all, I remember when Satoshi created bitcoin core wallet, it has private keys, and if difficult to use for a start there are still many wallets that follow the rules of privacy like hardware wallets, if expensive there are still wallets that cost nothing than downing their software on phones and computers that follow the rules of privacy unlike third party wallet which has no privacy. I can not use third party wallets, not possible.
1) Every wallet has private keys. Otherwise you wouldn't be able to sign transactions
2) Using a desktop wallet does
not guarantee you privacy (e.g. electrum: the server you are connected to knows all of your addresses, your balance and your IP address. This makes it extremely easy to track you).
3) Hardware wallets are just the hardware. You still need software as an interface. If you are using wallets like trezors web interface, ledger live or electrum, your privacy is not existent.
Revealing your privacy makes your fund not to be private, also never use kyc payment methods
If I have conbase, and I use credit card or other payment method that have enough identity of me, my privacy is completely lost in connection to the bitcoin I bought with the card and also in connection to the wallet I used. Very possible this can be used to track any wallet or exchange I send the coins to. That is why I like p2p exchange.
Not necessarily.
You could easily mix the coins by either using a mixer or coinjoin.
This will break any link between your original coins (tied to your identity) and the coins you later have in your wallet (which you will spend).
The use of bitcoin ATM, best way to 100% privacy
I suggested another idea below how privacy can be 100% but I will like people to talk about this, I think with bictoin ATM for depositing bitcoin into blockchain through keys in wallets, I think this is a good idea to 100% privacy as p2p exchange may not be sufficient. P2P may not lead to 100% privacy.
You never get 100% privacy.
Privacy can't be measured in percentage. You always have to include the anonymity set when talking about privacy.
With an ATM where cameras are directed at you and required KYC for amounts larger than X (like a few hundred $?) and where people can observe you while using them, i wouldn't call that privacy.