IMO, the major weakness of this class combo is that you can't wear armor without suffering the arcane failure chance. Wearing that Breastplate of Command, you'll lose 25% of your spells, and there's really no way around it.
The whole point was to create an armored arcane spellcaster. I did some rough calculations comparing a spell sword to an armored spellcaster using still spell on all somatic component spells. The still spell metamagic feat essentially causes a loss of two levels in the spell casting class as every spell is one level higher. Compare the Spell Sword 10 to 10 levels of another spellcasting class (with +1 spellcaster level/level) Spell sword yields 5 spellcasting levels with the ability to wear Mithril Breast Plate as the best armor possible without losing spells. Spell caster yields 8 spellcasting levels with the ability to wear any armor (not to mention the two pseudo-lost levels can be used for spells with only verbal and material components - so not a total loss). The only downside then is the loss of BAB (assuming another class will give equally cool abilities as the magic schtik and handle) This is compensated by taking Sacred Exorcist which has the same BAB, and personally, I think the abilities of the Sacred Exorcist (especially for a paladin like character) are much better than those of the spellsword.
Given the liberal use of Still Spell, arcane preparation is a must - just another reason to take the MotAO PrC (for at least some levels).
If you are going to be in melee a lot, try leaving off the MOTAO at level 6 and uping sacred exorcist to 8, should get you two bab I think. I dont have my book here though, so you might loose something good with MotAO 6.
The reason for taking the 7th level of MotAO was to get access to Spell Pool III (7th-9th level spells) But as you can only get a number of spell levels equal to half your caster level, that ability may not be too crucial. In fact, I could probably lose 3 levels of MotAO, take an additional level in Sacred Exorcist and then take two levels in another class to get a higher BAB and better abilities
Auraseer - Dragon Disciple is very cool, however, I am pretty set on some combination of what I already have. For the DD to be useful I need to take 5 levels in it to get the size increase. Also, the PrC is much more of a nonspellcasting PrC. I had given it some thought and I would probably start taking levels in it as soon as I hit 9th level casting ability so that the bonus spells would all be 9th level.
So revised Character looks like this:
Pal1/Fig1/Sor4/MotAO4/S.E.8 with two additional levels of spell casting either in MotAO or some other PrC.
Chr
Str/Con
Dex/Int/Wis
Still Spell, Arcane Preparation, Cooperative Spell, Power Attack, Extra Turningx2, +6 feats (1 of which must be a metamagic feat).
Contenders for those feats are as follows:
Combat Casting
Combat Reflexes, Expert Tactician
Divine Might
Divine Vigor
Energy Substitution, Energy Admixture
Eschew Materials
Expertise, Superior Expertise, Chink in the Armor
Extend Spell, Persistant Spell
Improved Initiative
Leadership
Lightning Reflexes
Quicken Spell
Repeat Spell
Spell Focus, Greater Spell Focus/Chain Spell
Sculpt Spell/Enlarge Spell
I don't think cleave and great cleave are good choices because I will have lower level spells to take care of weaker enemies. Also, with Shield AoO are less of a concern, so taking sunder or any of the expertise-prereq feats that counteract AoO are not nearly as useful. I am skeptical of taking combat reflexes because most likely my dex will not be that high - I won't get that many additional AoO. Also, I am guessing that I would be casting True Strike pretty often to make use of Power Attack and my AoO will consequently be less likely to hit. However, the expert tactician/blink combo sounds pretty devastating. Given that I will be able to use Turn Undead 9+chr(mod)/day I was thinking that I either ought to boost that ability or take some of the divine feats to make use of all of those attempts.
With regards to metamagic feats, if I do take any additional I would want to tailor my spell selection to maximize their usefulness. I was thinking enlarge spell combined with cone AoE spells would be pretty useful because of the range-AoE dynamic of those type of spells (would probably then take sculpt spell to turn spells into cone effect). The energy Substitution would increase the diversity of the spells I could cast (less useful if I wound up taking the Shadow spells). Eschew materials might be useful as I would be wielding a weapon and shield and the dynamics of switching back and forth might be difficult. The extend spell would be useful for spell pool accessed ability buffers and the persistant spell would be phenominal with shield spell, haste, etc. Given that I have arcane prep. Quicken might also be very useful (especially for true strikes). If I do take chain spell I would probably also then take spell focus and greater spell focus in a school that I have a lot of spells in. Repeat spell - can you say TRUE STRIKE.
A couple of other things important to note - I would use leadership to get a dragon cohort (when I am of the appropriate level) at least a flying creature that can be used as a mount. This would make the fly spell far less useful - one reason why I did not select it. Also I could always polymorph into a creature with wings.
I was also thinking of the ambidex/multidex/feat chains. With alter self and polymorph self I could morph into creatures that have additional limbs, bite attacks, tail attacks, etc. Combined with Spiked armor and a spiked shield I could start getting quite a lot of attacks. This would not be nearly as useful until later levels when I had haste and could still cast spells while taking a full attack option - but I thought I would throw the option out there for you all to think about. Also, I don't remember if this is an ability or a feat but multitasking (where you can use diff. limbs to diff. things might also be useful).
For spells, it looks like I would go with:
1st - true strike, shield, magic missile, color spray
2nd - web
3rd - haste, blink
4th - polymorph self
5th - wall of force
6th - tensor's transformation, greater dispelling, summon monster VI
7th - limited wish
8th - mind blank
9th - time stop
I am not including the spells I will get from the exorcism domain from S.E. PrC. IDHMBWM and am unsure about the usefulness of mindblank. Will PfE and nondetection accomplish the same thing?
I was also thinking about equipment and think I should go with a ring of counterspells with silence as the spell. I will have vocal components in probably all of my spells. For See Invisibility I was thinking it would be better to get an item that did that, pay for permancy'ed version of it, or go with a higher level spell.