Definitely not necessary to go this order. Nostr is a lot more accessible in a matter of a couple minutes. Even if you're using an awful KYC exchange and sending a bank wire to fund your purchases it's likely going to take you a few hours to actually buy some bitcoin, unless you're given a hardware wallet and are nearby a bitcoin ATM. 

Besides, come to Nostr first, get a lightning wallet, and you'll likely end up getting zapped at least a few sats to start your stack anyway.