>>/10840/
> This episode really help set Pinkie Pie at her best
Seeing it now, it really is an alarming decline later on, both in terms of how quickly the nuances of her character were lost, and in terms of how drastically she changed. Pinkie was never my focus originally, so I don't think I was paying attention to it, but I think I understand a bit more of the pain of the Pinkie fans now. Fun fact, another of my several introductions to the fandom, Tauberpa, had Pinkie as his favourite pony, and I believe his friend Xanauzumaki's favourite was Fluttershy. I got a new appreciation for the both of them after getting into the show back then.
 >>/10841/
> What sort of spell does Twilight Sparkle have in her "25" magic tricks that is causing monsters to change there desire and possibly digestive systems?
I'd say transmogrification. That detail, at least to me solidifies my belief in the "spells as categories" theory I posited prior.
> what short of spells she can cast on the fly versus what sort of things she needs to read from a book before she casts it? 
In Ticket Master she teleports without meaning to, and in Winter Wrap Up she messes up the "come to life" spell, so I'd say those are examples where she tries to cast the spell from memory and it doesn't go so well. 
In addition to spells being categories of magic, I'd suggest that a good analogy for how Unicorn magic seems to work is music. You can remember particular pieces easily enough, and perform variations on them when you know them through-and-through (thus being able to use one spell in hundreds of different applications, as per my theory), but more complex pieces are advisable to perform with sheet music, i.e books with magic instructions. You might remember parts of the process, as Twilight did with the come-to-life spell, but if it starts going wrong, you'll want to have instructions handy.
> Does Rarity have a secret affinity for animals!? 
She does the same thing with the Diamond Dogs iirc - I think it's rather that she has an untapped potential of commanding people, that is to say, she rarely does it unless it intersects with her interest in fashion, but when she does people fall right in line.
> Funny enough, by creating chaos in Fillydelphia she still technically saved everypony the trouble from the damage caused from the town, even if they did cause havoc in Fillydelphia.
You know, that didn't occur to me. I know that's what happened in FiW, but as a result I assumed that was a joke from that show - I just thought in this they roll the Parasprites into the Everfree and the infestation in Fillydelphia was a separate, unrelated incident. Do we actually know for sure that those Parasprites made it to Fillydelphia? I think you're probably correct that it was implied, I'm just curious as to whether something actually confirms it.