I feed babies as many of the appropriate sized insects as they will eat in a couple of minutes at each feeding....which should be a lot more than 3 for a veiled.
I've never used commercial products for gutloading. I prefer to feed the insects (crickets, superworms, roaches, locusts) a good healthy diet of greens (dandelions, kale, collards, endive, escarole, mustard greens, etc.) and veggies (carrots, squash, zucchini, sweet potato, sweet red pepper, etc).
I dust at most feedings with a Rep-cal phos.-free calcium to try to balance the usually poor ratio of calcium to phos. found in most feeder insects.
I dust twice a month with Rep-cal phos-free calcium/D3 powder to ensure that they get some D3 without overdoing it....and leaving them to produce the rest of the D3 from their exposure to the UVB (long linear fluorescent Repti-sun 5.0) tube light. D3 from supplements can build up in the system but D3 produced from their exposure to the UVB shouldn't as long as they can move away from it if they want to.
I dust twice a month with a vitamin powder that contains a beta carotene (prOformed) source of vitamin A. Beta carotene can't build up in the system like prEformed sources of vitamin A can. There is controversy as to whether all/any chameleons can convert beta carotene but this leaves it up to the keeper to decide whether to give the chameleon prEformed vitamin A or not. Excess prEformed vit. A can build up in the system and may prevent the D3 from doing its job and push the chameleon towards MBD...so be careful not to overdo it.
Calcium, D3, phos. and vitamin A are all important in bone health and in other systems in the body and need to be in balance. When balancing them you have to look at the supplements used, what you feed to the chameleon and what you feed to the insects.
Appropriate temperatures also play a role in that they affect the digestion and thus, indirectly the absorption of nutrients.
Keeping them the way I do, female veileds usually live to be over 6 years old and males even longer...so all I can do is assume that how I keep them works.
Sorry for a rather long answer to your question, but I think its important to give the whole picture.