It depends on the UVB light you use, or if you use one at all.
If he has a 5.0 or better UVB bulb and it is replaced at least once a year and he can get within 6 inches of the actual bulb, then d3 can be used once every 2 weeks. Some people use it once a month.
The new trend, and it seems to be one that will stick, is to use Repashy Calcium PLUS which has very low dose vitamin D3 so you can use it at nearly every feeding and not worry about 'Hrrmmm did I dust with d3 last week or 2 weeks ago?'
It is hard to keep track of unless you're ticking it off on a calendar.
Multivitamin, at that age, should be used every 2 weeks as well. When he is an adult, males only need a multivitamin once a month, or on ONE feeder just once a week.
I prefer to do the 'one feeder once a week' to keep things in balance. Going an entire month without any multivitamins, and then over-dosing them for one day out of the month seems a little unbalanced IMO.
Another thing you will want to do is Vitamin A on ONE feeder ONCE a MONTH. Get a Retinyl palmitate & Halibut Liver Oil gel capsule, pierce the capsule, and put ONE drop onto a cricket and make sure he eats it. This really helps with skin, eye, and tongue health. Never do all this stuff on the same day, as Vitamin a, d, and e can compete for absorption in the gut and will cancel each other out.