Also, Hunters? Kaladan? What?

Well prepare for a ride:

First we got 6 books by Frank Herbert, in 3 blocks i would say:

1. Dune, Messiah of Dune, Children of Dune, the book that started it all and its two continuations, pretty straightforward story of Paul Atreides.
2. God Emperor of Dune, time jump 3000 years forward, main character is Paul's son, Leto, though not from his PoV. Imo best book in series and thus best sci-fi book ever. Do require reading of previous ones.
3. Heretics of Dune and Dune: Chapterhouse, again timejump 1500 years past GEoD. Definitely weaker than previous books and unfinished

Then there is Dune Encyclopedia, noncanon, but was accepted by Frank, nowadays pretty forgotten and impossible to get in paper form. Somebody made the pdf though so it's accessible. Highly incompatible with all Brian books.

And finally the Brian books, though i seen there are some comics sidestories too, which i didn't read, so there are the books only here. I would group them by the trilogies, since he write them as such (except two), in suggested order of reading after the original Dune:

1. Dune 7: Hunters of Dune and Sandworms of Dune - they do include some parts of lore from Butlerian Jihad trilogy, but it's not necessary to read that first. Those are actually kinda fitting end for Dune, on par with last two books of Frank.
2. Legends of Dune: The Butlerian Jihad, The Machine Crusade, The Battle of Corrin - the foundational event of entire setting, 10000 years before the original Dune. First book of three is filled with too much nonsense and body horror but it gets better later. That is, i still lament how the suggested magnificent Greek tragedy of the original Butlerian Jihad is turned into yet another skynet war.
3. The Great Schools trilogy: Sisterhood of Dune, The Mentats of Dune, Navigators of Dune - closing up of the Jihad trilogy. Actually quite good.
4. Prelude to Dune trilogy: House Atreides, House Harkonnen and House Corrino - prequel of original Dune. Pretty pulpy but not bad.
5. The Caladan Trilogy: Dune: The Duke of Caladan, Dune: The Lady of Caladan, Dune: The Heir of Caladan - follow up for the prelude, books trying to fill the inconsistencies between Prelude and old Dune and those in the old Dune itself (mainly how is that the honorable and straightforward duke Leto so greatly feared by emperor). Not bad, though emperor is presented as the lousiest and most annoying piece of shit this side of Ramsay Bolton.
6. Heroes of Dune: Paul of Dune and The Winds of Dune. No, just no. It's remarkable just how much trash are those two books compared to all the others. They were so shitty even authors stopped after two books and only just released the third after i assume complete rewrite since it took them 14 years.