Now, I've heard a number of different ranges for this. The kuni guide says 23 yards, and I think I saw 15 yards quoted elsewhere. That's a pretty big discrepancy.
There was a hotfix which altered the flight time of some of our spells. Some sources might still show the older higher number. Its very close to the boss I would guess anything higher than 15 yards you should be fine. If are worried about it go to a target dummy and try it out.
Synergy between spells from what I understand is when i cast FOrb, i always throw in Blizzard after since its instant cast with the new trait, i always use 2 Blizzards with 1 FOrb cast as it helps reduce cooldown on FOrb. Frostbolt crits reduce cooldown on IV.
No no no ... Don't cast Blizzard just because Freezing Rain buff is up. Make sure it's worth casting first (i.e. 2+ targets).