The weekdays sell out later than the weekend, but they do sell out. A sold out weekday and a sold out weekend will still have the same number of people going to the exhibit.
Yes, but a lot of people who buy tickets on a weekday will be planning to go after work, since the venue is open until 10pm. So going at 1pm on a weekday should be much less crowded than 1pm on a weekend, when most people are free.