I would have to call maneuvers "special attacks that depend on size" (even though it is a bit upsetting that there aren't any given as examples), so yes, it should apply. And since Titanic is an effective size increase while enlarge person is an actual size increase, they stack.
Technically you have this section of the rules.
Combat Maneuvers is clearly under that section, so it's a cinch. Unless I'm missing something? The heading fonts are a bit odd on d20pfsrd, it may be more obvious here.
Hmm, if you count as one size bigger for combat maneuvers, then it should also affect your CMB, correct? The "Special Size Modifier" of the general CMB calculation should kick in.
It would if it said "you are considered one size bigger for combat maneuvers," but in fact it says only "A creature wearing titanic armor is considered one size category larger for the purpose of using or being affected by special attacks that depend on size". So you can bull rush a creature one category larger than you otherwise could, but you don't get a boost to your CMB.
(Also, if it were to boost your CMB they would certainly say so explicitly, rather than leaving something so important to only people who manage to read between the lines.)