I edited your post to fix those strikeouts for you.
How will I know if I'm not really ready for this? When will I know—during my workout, or tomorrow night when I'm in too much pain and too exhausted to talk to my dinner guests?
It is very unlikely that you will be sore and exhausted the night after. However, you will know during your workout. 7 to 8 is just the guideline. If you can't do 7 and can only do 5, for instance, that's okay. You can just adjust the other days as needed. You'll get better at doing more of them as you gain experience using the method. Much of it has to do with how well you handle the warmup and acclimation.
Now, it is very important to realize that your choice of weight for the singles falls all the way down to 90% of your relative max. A lot of people seem to think they have to keep all the singles on the high end. You can skip around within that ten percent as needed and even if all of them are on the low end that is perfectly fine. When you can't skip back down to the lowest intensity allowed and do a good rep, you'll know you're probably done ("probably" because this is related also to how early in the session this happens. If it happens very early, it can just be a problem with acclimation).
How long do most people who use this stay with it at a time? 4 weeks? 8 weeks? I can imagine that I'll want to shift my emphasis after 4, but I'll see how I feel.
It is certainly possible to run it back to back but you should definitely see how you feel.
I know that it can be a bit daunting, given the message that has been shoved down most trainees throats for so long by those authority figures that this range of intensity is so very advanced and you shouldn't use it very often, etc. and so on. But you'll see once you do it.
The trick is to really be aware of the quality. You are not supposed to bull through a singles scene session when you see you performance going completely downhill. As I have said before, we are not looking for perfect reps, as this is near maximal training, but we are also not going for an all out PR. You have to use your best judgement. I do not want you are anyone to get hurt, especially using my advice. But there is nothing in this that is dangerous. In fact, it's going to tend to have less potential for being injury producing in it's own right than higher volume "heavyish" training like 5X5's or, yes, 5/3/1. Do this at your own risk, sure, but risk is always a part of strength training. Here, the risk is quite manageable.
It may be that your first few sessions with this are not exactly up to your expectations because there is a bit of learning and experience involved in dialing this in. But doing that has it's own rewards since what you learn here will follow you into other types of training. This is a very 'experiential' way of training and the trainee absolutely MUST pay attention to their performance and what is going on with their body. There is nothing rote about this. Even if this first session doesn't go perfectly, you'll probably still have loads of fun with it.