Your method should work fine, it does take some time to get the colony thriving, just be patient. Generally they like darker areas, I always just used a bucket with a lid, with some holes drilled in, and raised them in a mixture of bran, pronutro (plain) and normal flour, about 1/3 of each, with a couple bits of apple or carrot on the top for the adults and worms to get some moisture. Change your fruit out at least once a week to prevent it fouling and going mouldy, and stick the whole bucket in a cupboard or in your garage. They prefer warmer places than colder, and soon you will have plenty. I used to seperate them out using a sieve and ice cream tubs to make smaller colonies, with worms of various sizes, so you have several colonies at different stages of growth. you can always fish out some of the white pupae and put them into a new colony, I found there were times when the worms would eat the developing pupae - probably looking for moisture. A couple of empty egg cartons on the top makes some nice hiding places for the adults.
You can do a similar setup with roaches or crickets as well if you ever want to, a large bucket with shredded newspaper and plenty of egg cartons for them to hide in, and regular greens/fruit to feed them, soon you will have tons of micro crickets. I used to walk around after a rain and catch the large black garden crickets and breed those. Very sustainable food supply once it is going. It does get noisy, so definitely not something you want to keep in the house