Actually, I'd recommend against DMM in most cases, just because you cannot get enough turn attempts to use it effectively. It's what, 5 TU's to cast a DMM Quicken spell, + 1 TU to gain an extra swift action? You end up using one less TU per spell than a DMM Persist cleric, but you have to cast your spells more often.
Since you're going for a more martial route, definitely take power attack. Extend spell is worth it at low levels to keep your minute/hour duration buffs up more, but if you're starting higher than level 6 or so don't bother. Martial Study is particularly good because you can use it to grab a Shadow Hand maneuver as a prereq for some of the higher level ones, but more importantly it adds Hide to your class skill list permanently - fantastic for meeting the prereqs for RKV.
Practiced Caster cancels out the lost CL from Crusader and RKV.
Otherwise, pick feats that complement your primary function. As an RKV, you can either focus on your spells or on your maneuvers, so pick feats that complement the role you want to focus on.
When in doubt, Extra Turning.
