OOH warlock questions. This I can do.
Hideous Blow : When asked, Sage Advice 'officially' ruled that as an invocation it DOES provoke AoO's. When asked for his take on this, Richard Baker (The writer of Complete Arcane) said "That's bull, it's a mellee power".
So you can either side with the sage who routinely makes bad decisions.. or the guy who wrote the class.
# of Invocations of each level:
3.
If you look at the chart, you gain 3 least invocations, then at level 6 you gain a new invocation and can then choose from Lesser as well.. however you can't trade a lower level invocation for a higher level one later on (Just like a sorceror couldn't forget a 2nd level spell to learn a 3rd level spell). This happens every 3 invocations, so you get 3 of each grade before proceeding to the next grade.
There's also a feat in complete arcane "Extra Invocation" that grants you an extra invocation of any grade other than your highest.
At lvl 12 you have 3 Least, 3 Lesser, and 1 Greater invocation, plus any bonuses from taking the feat.
Empower and Quicken SLA both state "Choose one of the creature's spell-like abilities", so yes you have to choose one when you take the feat. I would suggest Eldritch Blast.

Though Quickened has many fun uses with warlock invocations.
Monks suffer severely from MAD.
Wisdom for AC and uses of stunning stuff, Dex for AC any any ranged stuff(as well as bonuses to reflex saves), Strength for damage and accuracy, and con for if they get hit.
Pretty much they need to dump int(which means low skills), and charisma(which means no one likes them). And then they still have trouble keeping up with the epic weapons and the like as players level up... as well as issues when caught flatfooted.
Except that the monk AC bonus specifically states "These bonuses to AC Apply even against touch attacks or when the monk is flat footed"
I agree with the rest though, Monk's a good dip class at higher level, but needs multiple good stats.