All the ones I have had could take a feeder about 2/3rds there size. So at that size feeder guppies should work fine.
I have never had any that were smaller than my pinky finger in length
(2-2.5") though.
Feel free to try as many dead foods as you wish, but be aware that there have been many cases were these little guys have starved to death before conforming to eat dead foods.