I'm in the same position as you after the 1.6 update, returning after a couple of years break. I played a bunch of 1.6 sandbox over the Christmas break and installed the following main ones for a career save. As far as I've tested they all work together in 1.6.
TAC life support and MKS.
Remotetech
EVE, scatterer, texture replacer, distant object enhancer, planetshine, KS3P (need to feck about with the config to make it less dark).
Flight Manager for Reusable Stages.
Mission Control 2 and s bunch of other contract packs.
In addition , the usual "good housekeeping" KSP mods. Flight engineer, alarm clock, transfer window planner etc.
I wanted to install Astronomer's Visual Pack but my laptop can't really handle it.
I looked at Kerbalism played a bit a really liked it; but it's not that friendly with other mods, hence I chose TAC instead.
The planet packs don't work as yet. Kopernicus isn't updated to 1.6. I'm torn between Galileo or Whirligig.
-edit KOPERNICUS IS UPDATED!
Can anyone chime in on a good planet pack?