You need to be clear about your threat model. Right now everything you do on monero is opaque for now. In 5 years or 10 years, it might be visible. Is that okay?
Using the same exchange for both sides of your transaction adds a lot of operational risk, they might see your IP address, they might see the transaction size, they might measure your typing speed, browser fingerprinting etc etc etc
The wallet you use may have some peculiar indication and its transactions, that can make it more easily stand out.
I recommend reading the monero white papers, they go into a lot of detail about rings and so forth.
So, if you're just trying to obscure your VPN purchase, your protocol is fine because the risk is low.
If your life is in danger if this gets connected to you, then you really need to come up with a very clear threat model, and figure out every step.
At a minimum, use two different exchanges for both sides of your protocol, transfer from one wallet to a different wallet on the monaro side so that you get different transactional fingerprinting.