Welcome to the forum!
I dust my insects at almost every feeding with a phos free calcium powder lightly to help make up for the poor ratio of calcium to phos found in most feeder insects. I dust twice a month with a phos free calcium/D3 powder to ensure it gets some D3 without overdosing it and leaving it to produce the rest of its D3 from its exposure to the UVB light. D3 from supplements can build up in the system and lead to health issues. UVB produced from exposure tomuvbto won't as long as the chameleon can move in and out of the UVB at will. I dust twice a month with a vitamin powder lightly that contains a prOformed (beta carotene) source of vitamin A. PrEformed sources (palmitate, retinol, retinyl) can build up in the system and should be used with caution only when needed.
You can feed it as much as it will eat in a couple of minutes at each feeding until it's grown if it's a male. Don't let it get fat though. For a female you have to be more careful not to overfeed it because it will likely produce a huge clutch of eggs. Female veileds can lay several clutches a year even when they have not been with a male. Does it have tarsal Spurs?
The insects should be of an appropriate size.
Any more questions...just ask.