1. Start with a nightmare via LPB, for Astral Projection and Etherealness at will. Sure, you can cast those, but why bother, when you can get your cool fiery mount to do it for you with a much lower level spell? Make an astral projection duplicate and keep both your original body and the silver cord well protected via Craft Contingent Spell.
2. Get all the usual buff spells and contingencies necessary. Layer what you can. Go ahead and start by surrounding yourself with a Wind Wall, inside of which is a Prismatic Sphere, inside of which is an AMF (excluding you via Extraordinary Spell Aim), inside of which is an ethereal you, protected by every contingency and defensive spell you can think of. (Some nice ones from Complete Mage include Energy Absorption, in case he finds a way to nuke you with his spell traps, and Karmic Retribution, so that he has to save or be stunned just for trying to attack you.)
3. If you don't want to use Gate, then go ahead and Summon Elemental Monolith. Direct it to sunder your enemy's bow or arrow quiver. Then stand inside your Rainbow Magic Shell and laugh.