K and meth are pretty common; I was in the "party/club" scene for a long time 01-05 and we used K/crystal (meth)/G and molly every week. we used the meth to stay awake and the rest to do exactly what you know them to do, so yes, it would be OK for a come down but what makes you say K!? are you looking to come down and go to bed or come down and kinda get that K type feel?
a benzo would probably be better if you wanted sleep but K would be fun too if you wanted to get in that K feel; w/ the meth (well, you are almost done now) but with K and meth at its top, the K is a bit weaker I always felt, so I'd take much larger bumps (I never shot K, only sniffed).
either way, you are fine w/ all that was mentioned. this is under the assumption youve done the other drugs you mentioned before besides the meth.