Without extracting the air, you will just be blowing hot air around the room. Also, you need to extract the stale air so that fresh, co2 laden air is drawn in. And yes. 250 will be ok for veg (get a MH conversion bulb) but you really need a 600 for flower in a 4x4.
You need a 6" fan, at least 400 cfm for that. Even just the 250 would need a 4" fan. You will also need a filter if stealth is an issue.
I'm running a stealth 250w 2x2 scrog grow at the moment with a 6" 425 cfm fan and I'm struggling but my ambient temperatures are high.