Air gets into the tent by the negative pressure created by the exhaust fan pulling air out. As previously stated, slight negative pressure is desirable. On your tent, you want to open one of those vents along the floor and this will be what is a called a passive intake.
You want to open a vent on the opposite side of your exhaust port so air is pulled in across your plants. Air takes the path of least resistance so if you have a vent open directly below your exhaust, it just pulls air directly up. Of course your circulation fans inside (which stay on all the time) will move the air around, but I still think opposite is best.
You could put a booster fan on this port to blow air into the tent, but it is not always needed. Imo it's just one more piece of equipment to add heat, use electricity or break.
As far as blocking light, I use the round port opposite of my exhaust and have some round flexible ducting about 6feet long inserted into the port and the draw strings tightened around that. This extra flex tube is then coiled into a circle to prevent light from taking a direct path into the tent. This tubing is also black on the inside to prevent any reflection. If you do not like this idea, you can build a light blocking box out of cardboard and tape to cover the port and it serves the same function - letting air in, but not light-google will show you how to build it. There are also products called light baffles, secret jarden makes them, but they involve cutting into your tent but the plus is you can put it wherever you want. To me, the long, flexible, coiled up hose is the easiest and cheapest alternative.