I don’t think it matters if you do the night visit before or after the day visit; it will be lovely either way. Definitely buy the ticket for the Nasrid palaces — this is the spectacular part of a night visit. You can purchase the Generalife ticket as well if you’d like to see the gardens (tickets are pretty cheap), but make sure you do see the palaces.
And it really doesn’t matter what day of the week you visit. They tickets are limited to the same total number of admissions each day, and they almost always sell out. So, regardless of the day, there are about the same number of people.
It won’t feel crowded except perhaps when you first enter the Nasrid palaces for your timed entry. Even then, people tend to spread out, and over your time inside those buildings, it will eventually be less of a crush than it felt at the beginning.
I second Carol’s recommendation for a guided tour. We have also used Margarita (and also a partner of hers on a second occasion when we were traveling with different companions). The service is not terribly expensive (around 120 euro for 3 - 4 hours), and the guide’s knowledge will greatly enhance your Alhambra visit, in my opinion.
Enjoy the Alhambra and your visit to Granada, one of my favorite places anywhere. Five days will be wonderful and you will have plenty to do and see — don’t let anyone convince you it’s too long to stay there!