Guppy and Cory tank

Hi! Finally got around to setting up my tank after a several years hiatus.

I’m planning on adding guppies and a few Cory catfish.. do you know which I should add first?

Also, my tank’s been running since Saturday night (there is a piece of wood I’ve bought that was inside a tank at Petco.. not sure if it helps build bacteria). how long should I wait to add fish, in general?

Thank you!