Ventilation

You might get away early on by opening the tent but that is only a short term way to get by. As you get into flower and run lights at higher power there will be more heat generated that needs to be taken away. You will also need to keep the humidity down during flower to avoid mold (bud rot). I use AC Infinity Cloudline fans with the digital controller. Top of the line and expensive but it makes taking care of your plants much easier. I just set max/min temperature and humidity levels and the fan turns on and off to maintain the tent where I want. My fan turns on at 29c and the temp peaks at about 30.5c. During flower I have my fan turn on at 55% relative humidity. You can also use a non-smart fan but observing your tent weather and finding a fan speed that keeps the temperature and humidity where you want. If growing where smell can be a problem get a carbon filter for your fan. Most websites show the fan and filter hanging in the top of the tent. It can be difficult to hang by yourself and it takes up a lot of room in the tent. I set my filter on the floor outside the tent, open side up. Then I use a plumbing rubber boot (sewer pipe coupling) to attach my fan on top. Then out of the top I use another rubber boot coupling to attach thin wall PVC drain pipe going straight up. Then I press on a 90 degree elbow fitting and then a short piece of pipe (now going horizontal) which goes into the tent. This way your fan is outside the tent freeing up all the precious room inside the tent for your light and plant.

Probably depends on the situation...Ventilation is there to control temperature and humidity. Too much or too little of either is bad. So it'd depend on your local conditions, what kind of heat your lights are generating, etc. Ventilation systems aren't that hard to set up...a few parts is all it takes...