Look like you did your homework, read a lot, I've did that too for my first grow (my old dream in my signature). Good idea to germinate the other seed right now ! You now really have a chance to have 1 female plant, always 50% chances of being a male. For the ventilation, I'm with you on the exhaust fan but you could make a passive intake. Humidity can, later on, be a problem if it don't go down... When flowering there is a high risk of mold with such %, just hope the fan will get it down.