Want to fiddle around with EHT development. What do I need?

Dear everybody, I would like to play around with developing on/for/with ETH. If I read the dev portion of the website correctly, I do need and ETH "account" meaning a private/public key pair / address. Correct?

Do I absolutely need a wallet and phone to get one, or can I do that solely online somehow?

Is there anything else I would need (not any libariers, I can find those)?

Sorry for the very beginner questions. :/

Best, -a