Finishing my Mageslayer...

[WeaselGuy]

So, for an upcoming game, I decided to dust off a concept I had floating around for a while, but I need a little help optimizing him a smidge...

Whisper Gnome Spellthief 9/Occult Slayer 5/Suel Arcanamach 6

After racials, stats are Str16, Dex18, Con14, Int14, Wis13, Cha14

Feats
Using Otyugh Hole for Iron Will
1-Improved Initiative
3-Weapon Focus (Spear)
6-Combat Casting
9-Combat Expertise
12-Improved Trip
15-Knock Down
18-Combat Reflexes or Master Spellthief maybe...

So, how does it look? Anything you would do differently, while maintaining the feel of a light skillmonkey focused in taking advantage of spellcasters?

My skills are, before racials and modifiers, Concentration(12), Disable Device(23), Hide(18), Jump(4), Knowledge-Arcane(23), Move Silently(18), Open Lock(12), Search(23), Spellcraft(23), Tumble(18), and Use Magic Device(12).

3.5e, all first party publications allowed, including campaign settings.

[Toshiro]

I would suggestion getting Mage Slayer feat (Complete Arcana pg. 81) it gives you a +1 to will saves and spellcasters can't cast spells defensively. The follow up feat to that is Pierce Magical Concealment (Complete Arcane pg. 81) which allows you to ignore defensive spells and SLA such as blur, darkness, invisibility, and mirror image. Though you would need Blind-Fight to acquire the feat, but this is the standard lock-down, mage slaying feats.

As for other notable things to consider. Another prestige class to consider is the Witch Slayer (Tome of Magic pg. 67). It gives really neat abilities such as Mettle and Momentary Disjunction to disrupt spells. For weapon of choice, if you're going for a trip build, once you gain levels in Occult Slayer and your DM allows retraining, retrain for Weapon Focus for a Guisarme. You won't be able to use it because Spellthief doesn't have proficiency with it, but the Occult Slayer gains martial proficiency. A reach weapon that gets a bonus while tripping? Yes pls.

[WeaselGuy]

If I redo it as cleric 1 with celerity and trickery domains, then feat rogue 7, occult slayer 5 and witch slayer 5, this is what I get...
I have a decent number of points in disable device, hide, listen, move silently, open lock, search, and use magic device, with enough points in knowledge arcana, knowledge religion, sense motive and spellcraft to qualify for PrCs.
At 18, I have a 15 BAB and 9/7/12 fort/ref/will.
I have improved initiative, weapon focus, short haft, combat expertise, improves trip, knock down, mage slayer, blind fight, pierce magical concealment. By level 12, so feats for 15 and 18 still available, as well as 2 more class levels, a decent template or 2, or a level adjustment for something other than whisper gnome.
Thoughts for templates occur to me as shadow walker and dark. /shrug
I've been staring at my notebook and kindle for so long, I'm starting to go crazy second guessing myself... someone save me...