As the 11 Hex/3 BG/16 PM already has a bit low AB, the Hex/Monk/PM would have even lower AB becouse Monk gets less AB than BG and dual-wielding further reduces ab by 2.
Being able to dual-wield you'd also need to spend 3 feats on Ambidexterity, Two-weapon fighting and Imp. Two-weapon fighting and adding monk generally means you're dumping shield and trying to raise your AC with Dex/Wis and that needs weapon finesse aswell, so that's 4th feat spend.
All that added up just means you're sacrificing AB/Dmg/Feats for some AC/AttacksPerRound on a build that already has good AC, but lacks in AB so the extra attacks are not too likely to hit when that low AB is lowered even further.
About the GSF feats and granting spells you need Wizard/Sorc levels for that and they're nice as extra stuff for mages that typically just watch their summons/buffed party members wreck things while saving their important offensive spells for critical situations.
http://wiki.nwnarelith.com/Warlock
If you're really interested in magic pew-pewing there's always the Warlock, fiend- or feylock.
Both have selected list of spells on infinity cast(so you can just cast them infinite amount of times).
Eldritch Blast which is (1d6 + 1)*(Caster Level/2) so pretty potent and as you level you unlock different dmg types with both types of warlocks getting access to magic dmg from 12 onwards, which goes pretty much through anything.
They mainly differ on their list of spells and the fact that Fiendlock has a fiend they summon that grows in power as they level while they feylocks have a bit more potent spells, even getting access to haste(which they can only have active on 1 other person besides themself, resulting in pretty much unlimited haste on you + 1 friend of yours).
Both varietys warlocks can get powerful on a quick windup, but the feylock is a bit better at that. Or they can just straight up blasting eldritch blast the moment they wake up, which is fine too.
Warlocks typically build for Epic Dmg Reduct feats(Which is now easier since it only needs 19 con) that combined with their Dmg immunity boost means they can take bit of a beating even thought they are 'casters class'.
If you want more info on warlocks just try the link or ask.