Yes that will be enough. Now I will tell you why I dont like to put suplements in the cage, because they atract humity and at least here when exposed to air they become shoggy and spoiled really soon
I haven't actively dusted my mealowrms in years so IDK. I keep a mealowrm colony and just dump calcium and vitamin in the mixture. The mealworms roll around and eat the stuff and they coat themselves. I also leave a little dish of calcium in the enclosure. Some people think its stupid and unescessary but my leos do actively eat the stuff.
what type of heater? if its an undertank heater id go with a thermostatically controlled unit .justa dimmer would be hard to accurately measure the current temp.
I'm getting an undertank heater and a thermometer to make sure it doesn't get to hot. I've heard that on most UTH you can't control the temperature and you need a lamp dimmer to control it.
As far as the heating goes (for your sake, I am certainly no expert) I would use a lamp. I bought a pad for my Snake but I've never used it. Seems like a fire hazard to me. Then again, it's on an unsealed wooden shelf, so...