Firstly, welcome to the rabbit-hole.
Do ALL purchases of XMR get the same privacy treatment?
Broadly speaking, yes, all Monero transactions have the same level of privacy.
I use the word "broadly" because privacy extends beyond simply what's recorded on the blockchain. For example, if you buy from someone giving them your real identity, they have your identity, a wallet address you gave them etc etc. This is why you'll often see people asking where to buy Monero without KYC. Similarly using anonymity networks such as tor/i2p; the aim is to not divulge any information that can be used to link you to a transaction. So if you transact giving away your identity or things that can be used to help identify you, like your IP address, then no privacy is not the same as someone who transacted over tor and bought without KYC.
Said another way, can I "carefully and safely" buy BTC or another crypto, then exchange it for Monero with the same privacy as if I buy Monero directly?
By using any transparent (i.e. Bitcoin) cryptocurrency you of course have a trail up to the point you get your XMR. The trail ends there though if your forward transactions aren't simply from the same exchange you purchased, i.e. you withdrew your XMR off the exchange to your desktop wallet. If you didn't do this of course the exchange has a record of all transactions you make.
So however you buy, make sure you spend from your personal wallet, not some exchange wallet.
To summarize, on chain the transactions have broadly the same privacy guarantees. Where you buy and how you transact are not — a non-KYC, P2P, tor/i2p, XMR->XMR transaction has much stronger privacy than other routes.