If a person stopped reading the X books around the time Hickman's run was coming to an end, where would they pick up? I don't care much about any unimportant side stuff. I'm just interested in knowing how everything played out with Orchis and about what ultimately happens with Krakoa.
The Orchis stuff was not developed that well to be honest, they kinda became generic X-Men villains and even though they are a still a formidable foe, I didn't find it very compelling once Hickman left. Regardless, if you really wanna read all the things related to them, those happened in Duggan's X-Men, specially after the first 3-6 issues which are more stand alone missions and set up.
The overall structure of the X-Line without Hickman was basically:
Duggan's X-Men: the superhero book of the line, with Orchis as the main antagonist.
Gillen's Immortal X-Men: the Quiet Council and "main plot Krakoa" book. This includes a heavy dose of Gillen's own pitch that heavily influences the direction of the overall Krakoa story.
There are two big events before the current events: A.X.E.: Judgment Day and Sins of Sinister. I thought they were dope reads but I wouldn't call them essential, you could easily get the gist of it via Wiki or Youtube if you don't want to be bothered.
To me, the legit follow up to Hickman's departure ("Inferno"), is Rise of Powers of X, that was out last week. You would be
about a bunch of shyt regarding Orchis and Krakoa, but the main plot threads Hickman left in Inferno are finally being adressed in RoPoX.
PS: I know you said you just wanted to know about Orchis and Krakoa but you are doing yourself a disservice if you don't read Ewing's X-Men Red