I didn't use Coinbase, but based on how centralized exchanges work, some things that come into my mind are:
* afaik Coinbase asks for KYC, make sure you pass that and don't get surprises when you want to withdraw
(as alternative you can look for non-KYC exchanges, usually decentralized ones, but those need a different learning curve)
* depending on the amount you'll be buying the withdrawal fee from Coinbase to your own wallet may or may not hurt (it's a fixed fee and on small amounts to withdraw it can be seen as significant fee)
(again, there's the already mentioned decentralized exchanges, but also the OTC exchanges which have worse exchange rates, but together with the withdrawal fees it may get less expensive for small amounts)
Sorry if I'm confusing you more than I help you. If you want to keep it simple: pass KYC first, don't withdraw very small amounts, instead withdraw after more smaller buys if it's the case.