Full details on the Relayer Wiki Page.
Keep critical stats off slots you may swap out. For example, Bracelets of Binding (wrist) are frequently equipped at champion spawns for teleportation — don’t put stats there that you can’t afford to lose.
Protection and Vampiric Embrace reduce resistances. If you keep them active, plan extra resists to compensate. Toggling these buffs adjusts resist caps in the character sheet; the status bar caps at 70 (the actual in-game maximum).
You may not want to max Physical Resistance — Reflect Physical Damage scales off the physical damage you take. More damage taken means more reflected. Just make sure you have the HP and healing to survive.
There is no hard cap on HP/Mana/Stamina regen, but returns diminish sharply beyond the configured cap. See the diminishing returns thread for details.
These attributes are worth maxing on every armor relayer (use the Prep button to set them all at once):
Total: 303 SP per slot (fits comfortably in a Normal weapon with a few Leveling Deeds).
Plan your UO:EX relayer builds across all equipment slots.