I smell... chicken

Is this going to be a series?

Totally Scootaloo.

He will train all of the CMC Like his own slutty Charlie’s Angels

Honestly this just felt like an odd anal fixation fic

This was enjoyable. A few weird ideas here and there and you should work on your grammar/spelling and proofread your stories more. But other than that, it was a good read. You conveyed the feeling of using the opportunity to have sex with a filly who is neglected by parents and big sister well. Slightly questionable what happened there, especially when he stuck his finger into Sweetie's anus without asking first. But that he taught her how to cook and some other things show that he cares for Sweetie even without having sex and that he isn't seeing her as sex puppet and Sweetie was okay with it and liked the sex, so the situation improved.
Still, you should avoid certain awkward ideas. The crab pony attack was fine, but the way you described it happened too sudden and this made the entire event too random.
The way you incorporated a musical number, while creative, feels off when thinking on it what we've seen in the show. For one, the instruments playing out of nowhere does not really work, because the music during songs is just background music and naturally wouldn't be heard in Equestria. We never see ponies with instruments playing those melodies during a song or any other identifiable source of the music. Reading that part was a little hard and I was glad when I was past it.
For second, we've also gotten several clear signs for it that ponies of course remember when they sung a song. And there is no logical reason why the background ponies who sing as choir should forget it. I never had to say this about any MLP: FiM fic I've read, but this part made me cringe, just for how unrealistic and much too silly it was. Creative ideas are nice and even vital but, before you write them into a story, you should think them through and check if they really make sense. It will heavily affect the quality of a story if you don't.
Other than that, I liked the story and I'm going to read the sequel as well. The cliffhanger at the end is exciting.

You know, Rarity might actually approve...