What Boxer said, plus you don't need the Redding GRX die. If it was me I would stay away from Titegroup in the .40.
Good results for light to medium loads can be had with 231/HP38 it's the same and WST, Medium loads on up slower burning powders like Unique, WSF,Power Pistol, HS-6, and Universal do great. Longshot is a good powder too, but usually reserved for max velocities.
Your 5.3gr. load is a light load but if it works for you great.
When you say do you need to resize your brass like rifle, i'm guessing you might mean to trim the brass. No trimming is needed for straight walled pistol brass like the .40. You always need to resize your brass before reloading.