Bear in mind buying endler fry means you can't guarantee the sex and they will breed if you have a mixture. Depending on the type of endler, not all of them are able to eat their own fry (they are very small fish) and it won't be great for your betta to be eating them all, so you'll have to remove some. Some will inevitably survive and you may end up with more than you want. Also the females are quite drab.
You might be better off just buying 5 or 6 males.
Also, watch the betta with the shrimp. Depends how big they are really. My betta pecks at adult cherry shrimp but they can evade him, but he will happily persue and munch smaller ones. Then again he may ignore them. Can't always predict these things.