What is the chronological order of the episodes of xxxHolic? I've seen the second season so let's start from there. That's when it gets complicated.

Which episode came before which, and when?

I know there is a OVA called xxxHolic Shunmuki but it didn't interest me in particular. I also saw that there is a season called xxxHolic ROU but I did not understand what episodes it has (at the moment) or how many seasons are there in general.
1st Season, 24 episodes
2nd Season (Kei), 13 episodes

Movie "A Midsummer Night's Dream", This probably takes place somewhere during the 2nd season (60 minutes, essentially a long episode)

OVA Shunmuki, 2 episodes, also crossover with Tsubasa: RESERVoir CHRoNiCLE
OVA Ro, 2 episodes, occurs a significant amount of time after Shunmuki.