I don't recommend using a substrate or a fountain with veileds. Its too easy for substrates to cause impaction and some of the barks contain toxic oils. As for the fountain, they are hard to keep clean and germ free.
The UVB should not pass through glass or plastic.
Is the calcium powder you are using phosphorous-free? Insects generally have a poor ratio of calcium to phosphorous...so dusting with a phos.-free calcium powder helps to make up for it.
Although sweet potatos and carrots are two good things to be a part of the gutload, I would also add greens (dandelion, kale, collards, endive, ROMAINE letuce, etc.) and more veggies (squash, sweet red pepper, zucchini, white potato, celery leaves, etc.)
You can offer him small waxworms (but not too many because they are fatty) and small silkworms, small butterworms, phoenix worms, etc. to add variety to his diet.