You want to eliminate as many leaks as possible to keep the ppm stable when you're using CO2. Extraction fans should be timed so that they don't waste the gases by immediately sucking them out of the room. And don't forget that with abundant CO2 in the air (1000-2000ppm), you can let the temperatures rise slightly higher than you normally would and the plants will be less affected by it. In fact, I think the higher temperatures (in the 90s) actually benefit the plants under these circumstances. CO2 is heavier than air, so it'll naturally fall on top of your plants if the dispenser is located above them. Our houses generally contain 250-400 ppm of CO2 in the air we breathe... if it's possible, try to shoot for about 1500 ppm in your grow room. And if you're limited on how much CO2 you have available, I'd use it more in flowering than in veg.