Well when I researched this a couple years ago I found that the FSA used slightly different sizes in their carbon cranks vs alloy cranks and that only the alloy 24mm spindle ones where compatible with Shimano Hollowtech II, the carbon ones were slightly bigger and a few that tried had to be hammered in IIRC they were too tight, but I didn't try this. I ended up getting the 30mm version and had to buy their special bottom bracket to fit standard English threaded bb bike.

But that poses the question... Which type of SL-K light crank are you getting... they are available in multiple styles to fit different bb's. I have two SL-K lights and both are 30mm spindle, obviously won't fit a 24mm hole in Hollowtech II - you probably are aware of this just making sure.

Shouldn't be an issue putting on different co. chainrings as long as BCD same... I actually converted an SL-K light to a 1X chainring. Some companies claim to optimize their chainrings to their own chains so there could be slight noise or quirky shifting but I am not sure if this is really a problem.