Even after my monster binge I had no comedown, just very tired. A few days later and I'm still not experiencing any depression or such like that I expected. Would almost give you the excuse to do it again without thinking it was a really bad idea. That's not the case though, I've learned my lesson and I'm glad I have.
If you want to get to sleep I suggest stopping redosing a couple hours before you intend on sleeping to let it wear off and for your body to adjust back to some form of normality. Getting to sleep whilst on it is going to be really difficult. The few hours you spend shuffling around will only seem like 20 minutes. As for using benzos or GBL to end a session, I wouldn't know. I wouldn't like to use a knock out dose of GBL after being so stimulated, personally. I've woken up from GBL before and not be able to catch my breath so that's a personal dislike for GBL on my side.
It's a very easy drug to over do, one overly late redose can set off a really bad chain reaction. My advice would be to set a time you want to go to sleep and have your last redose 2-3 hours before that.
Have fun, use wisely and know when to stop. Don't go over, in my opinion, 600mg in a night and give it a break between using it (week or two minimum) even just so that it hits you like it should when you next use it.