What if I don’t have an existing ronin and metamask wallet, should I just import my trezor seed phrase (the 24-word seed phrase I have upon setting up my trezor) upon installing the ronin and metamask extensions? Or do I have need to create a ronin and metamask wallet first and then connect my trezor?
do not import your Trezor recovery seed to any 3rd party wallet as it can get compromised.
You can just pair your Trezor with Ronin wallet by exporting public keys.
So answer to your second question is yes, first create 3rd party hot wallet and then pair it with your Trezor.
see following thread for more information: