Hello, new member here

I'm replaying KH Final Mix on my steamdeck before moving on to either CoM or 2. I'm considering finally getting the ultima weapon keyblade as i never bothered, my question is...

I'm currently at Ansem Riku, should i seal Hollow Bastion's keyhole before farming? I know the worlds changes (enemies-wise) after that, is it a good move to start now or should i wait till the end to do it?

Also proud mode, why am i doing this to myself, it's the emulated ps2 version, i won't get any achievements to proudly show off my efforts.. sighs