my gar love nightcrawlers but they are all over 1' . My juvi gars get guppies and rosy minnows, and access to them 24/7 with the occasional day or 2 w/out. once they hit 1' i will start encourageing pellets into their diet but continue goldfish/rosys regularly approx 40% of their diet. the only frozen food my gar like is krill... and I haven't tried yet but am thinking of adding cut peices of fish to their diet from the market. the bones,guts, ect are all where the mins/vits are not so much the flesh, thats where the fats and protiens are.
bloodworms imo are worthless nutritionally and like giving potato chips to kids, they are a snack. and unhealthy, very little nutritional content to them. I would try mysis shrimp or break up krill instead. The only time i usually feed bloodworms is when a fish refuses everything includeing live blackworms, but then work to get them off them quickly. Ive seen fish "survive" on bloodworms and some wither away being fed large amounts, spiney eels are usually a great example of this.
Guppies breed like mice given the space. Ive never bred minnows but heard it can take awhile to build up a colony. my local LFS gives me a discount because i buy large amounts fo live feeders, most will if you ask. Particularly if you are a regular.