First thing to do is to pull the clutch cover and check the star piece on the end of the shift drum. Either the spring loaded roller wheel for the star has come loose or the star did. Chech these things first. If this is not it then it's time to dive a little deeper.
As far as gaskets go I buy just what is needed to do the job. For a complete tear down, Cylinder head and base gaskets, rocker,clutch cover, stator and center case gaskets. This is the best approach. The sets that honda sells have things that are some times not used and ya pay dearly for them.
Good luck and keep us informed.
Steve in SF
87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project