An oscillating fan hanging from the ceiling of the tent and over the light is not going to do what it is supposed to. You want the oscillating fan pointed at the plants to give them a bit of "wind" to help strengthen the stems and it also helps to remove heat from directly under the light. It would work fine to put a couple of non oscillating fans clipped to different tent poles if you can reach all the plants that way.
When you say vent fan are you speaking of your exhaust fan? If so, leave it on all the time. During vegging, plants need a continual supply of fresh air all the time the lights are on and in flowering, like MR1 mentioned, it creates the negative pressure that you need to keep odors contained. How large is you exhaust fan? I have a 6" Vortex in a space smaller than yours and it is not too much air exchange--I like to exchange the air in my space several times a minute. However if you have a larger fan than say 8" and you want less air exchange, buy a fan speed controller and set it where you want it.
Pssst, Hackerman, no bigger is not always better....