My sugestion is:
Start at both ends, modern and classic.
Modern path - Origins, Tour Of Duty, Day Of Chaos, Trifecta - and then you can wait for upcoming jumping point in 2000AD (most recent jumping point is this week Prog 1973 if I remeber correctly).
Classic path - Case Files, start with CCF5 and if this stories works for you collect onwards (from CCF 1-4 most essential is CCF3 so I suggest it as alternative start).