Odds are usually 50/50 for male/female from seeds from what I know (unless something is done to change it).

Good idea on the mylar, I was gonna suggest that before I saw your comment.

Be careful about the fan (since you said it was from an old comp) - I used to be a PC technician and I've seen lots of old fans overheat and die or get clogged from too much dust and crap. Keep an eye on it - don't wanna see you have any unecessary problems. You shouldn't need another fan for intake, just an opening to let fresh air in. The exhaust fan will lower the pressure in the growroom and new air will rush in by itself from wherever it can to replace the old.

What kinda light you using??