I'm all for non-standard templates but the combinations you're talking about don't go well together. There's a bit more to it than throw that skill on and gain all it's benefits, you need to think about factors like, swing speed, casting, interruption, healing, curing, damage, what level monsters you're fighting.
With no Tactics you won't deal enough damage to leech/live.
Focus Attack is 30 DI and doubles your 'Hit' properties on weapons. *I think* you can also only use it with one handed weapons, which equates to lower base damage.
Mysticism for a dexxer works best built for Stone Form. Stone Form works best for using bandages to Heal because you can't be Poisoned or have your Dex lowered. But it comes with certain penalties like -10 SSI. If you're intending to cast during combat you also then need to factor in the penalties from playing in Protection.
Ninjitsu for a dexxer works best for Mirror Images. Mirror Images work best at 4/6 casting. Other good uses are Animal Forms. All of this means being on foot.
Necro for a dexxer works best with either Vamp Form, Wraith Form, Curse Weapon, or a mixture of all three. If using the forms you're not using Stone Form from Mystic. Ninja/Wammys work well.