84F is fine if he's young, and you can raise it to 90F when he's a little older. And no, if the cage is a good size and the basking light is in one corner he should have enough options to move in and out and regulate himself properly. Veileds like a bit of heat and do well at about 90F under the basking spot - so long as the ambient temperatures can stay cooler. Is he in glass/wood or screen? The type of cage may dictate how warm you can go before the interior temps don't stay cool.