Regarding growing worms in liquid culture:
Good aeration is key to getting a high yield of healthy worms. Shake
vigorously, using baffled flasks if possible, and larger volume flasks to
maximize surface area/volume (e.g. 500 ml culture in a 2 liter flask).
Also, using E coli strains that are healthier than OP50 is a good idea, since
you can get a better yield of food. Grow up several liters of bugs in advance
(store in the fridge as a concentrate) so that the worm culture can be refed
as the worm population expands.