I'd recommend swapping Crit and Direct Hit around. You want to prioritize Critical Hit>Direct Hit>Determination>Skill Speed for your DRG build.

The skill speed aspect is highly dependent on latency and keeping within particular GCD thresholds (2.44 and 2.43 GCD rotations are more optimal in a raid environment.)
2.43 GCD = 782-848 skill speed
2.44 GCD = 715-781 skill speed

In terms of your second question, it was stated that ~2500 Critical Hit was the threshold where it will out-scale other sub-stats. Regardless of this, the amount of times your abilities crit depend on RNG and group synergy (SCH's usage of Chain Stratagem, AST's Spear Card, BRD's Wanderer's Minuet/Army's Paeon)