Best cross-class skills for leveling?

[Roth_Trailfinder]

I would recommend next:

Culinarian to 37 for Steady Hand II (Also very cheap to level), makes Hasty Touch even more amazing and helps with that extra Experience per craft

Carpenter to 50 for Byregot's Blessing

This. Very much this. What you do after this is up to you, but very very much Culinary to 37 then Carpenter to 50.