Do you want more power after stage 2?
k04 would be the next choice if you are wanting to be in the low 300s to the wheels. Its plug and play.
Next up would be to get a stage 3 kit which uses either a GTX28 or GTX30 depending on where you get it from. That should put you in the upper 300s to 400whp.
It really depends more so on what you are wanting to make.
If you are stage 2 you should have a intake and downpipe as a minimum. For k04 or above it would be recommended to get an upgraded intercooler, TOP and throttle body pipe, maybe add in the catback exhaust portion if you are going stage 3 to get a little extra flow through the system.
Depending on which stage 3 kit you get or what your power goals are you may need to do rods on your engine internals and possibly a lpfp