Gear mods can get pretty in depth, especially when it comes to a custom shop like Brian's or Vaughn.
IMO the best thing to do is to work backwards. Determine what you want in a pad and then see what the manufacturer can do to fit your need.
Here are things to think about, and I'm just scratching the surface here.
Pads:
Desired stiffness (# of breaks; internal or external or both, type of foam core insert, boot flex)
Soft or firm face (depends on how you like your rebounds)
Boot scoop shape (wide or narrow stance)
Sizing and where you want the inches (ie. subtract from boot to add to thigh)
Toe attachment method (inset or center), skate lace or elastic
Knee stack and calf wrap options (add/subtract inches to thickness, cut and paste parts from another line)
Sliding surface (Primo, jenpro, weave)
Glove:
Type of break
Tee type
Tee reinforcement
Glove palm reinforcement (game ready, pro, practice)
Backhand cuff shape
Palm texture/material, palm size
Wrist strapping (nylon, leather, BOA)
Blocker
Board firmness (rebound velocity)
Palm texture/material, padding (most modern blocker palms have some padding to alleviate stick vibration)
Palm size, hand position
Finger protection
Side board air pillow
Wrist strapping, backhand cuff shape