For stems and seatposts, just get whatever you like/can afford. They hold your handlebars and saddle in place, not much to it. Same can be said for handlebars I guess, but here you have different types (classic bend, track drops, compact, etc). I would avoid track drops and get some compacts.
You've got your definitions mixed up. A groupset refers to any mechanical or electronic parts that are involved in braking, changing gear, or the running of the drivetrain.
For stems and seatposts, just get whatever you like/can afford. They hold your handlebars and saddle in place, not much to it. Same can be said for handlebars I guess, but here you have different types (classic bend, track drops, compact, etc). I would avoid track drops and get some compacts.