You are very talented. The drawings are beautiful. It probably won’t be a problem with 2 plants and since it will be a constant flow of air humidity shouldn’t build up to much but I have seen many that exhaust to an attic create a nasty mold problem.
Is your attic vented with Ridge, soffit or gable vents? Will there be a control on the fan to lower the speed? The thing is I see many people vent their spaces but they don’t understand air pressure. All air you force out will need to be made up. Like the intake and exhaust on your tent for example. That air is coming from your room which is coming from your home. If it is 100cfm for example you will have taken all the air from a 10x10x8 room in 8 minutes. Not bad in the spring or fall months since most aren’t heating or cooling but in the middle of winter you will notice drafter windows and doors. The air is being brought in to make up what’s being sent out will be noticeable. Same with all alliances in your home that exhaust out. Furnace, fireplace, bathroom fans, dryer.