Yes, there are a lot of moving parts, but once you have an awareness about them all then you can incorporate a strategy in each area, which it appears you’re doing.
You ARE interviewing them as much as they are interviewing you, but it’s essential they don’t feel that way. If you give them the impression that they might not be good enough for you during the interview, you’ll hurt your chances significantly.
I’ve said that in social media forums before and gotten some upset feedback, so I’ll explain. Yes, you DO have to evaluate them, and I understand that you don’t want to look desperate, which is a fine line. Here’s what I’m referring to: from a very over simplified psychological perspective, if you’re the hiring manager, and you have two finalists to choose from, one says he would love the opportunity to work for you and position sounded great, and the other person said he would take the job but only if you can show him it will keep him challenged.
Who would you be more excited to hire? Or from the opposite perspective, who would you feel better about rejecting? (or who would be easier to reject?) Hiring Manager are just job seekers who happen to have jobs, they’re people, and they react to situations the same way you do.
I hope that helps.