IMHO, as someone who rode many a "B" session with intro riders, the biggest thing is to not get overly anxious and impatient.
The first two laps of the intro/B sessions will be under a standing yellow (no passing). The Control Riders' first job is to keep everyone safe. Going fast is secondary.
that said, they want to evaluate who is on track a bit before just turning you loose. But they also understand that the intro guys only get 40 minutes, and want to make the most of them. Personally, I'd rather go a bit slower than I wanted than sit on hot pit because someone wrecked. Patience is a virtue.
What you absolutely DON'T want to do is break passing rules. I watched an intro rider pass (me) under yellow, and when a CR came around both of us to reign him in, he passed the CR without being waved by. That resulted in an immediate "slash across the throat," and a long talk on pit road. The guy was fast, but impatient. Probably wasted half of his first session getting reprimanded, when all he needed to do was wait another lap before picking up the pace...
Regarding whether or not there will be a "B" spot open for Intro riders, If the day isn't sold out, then absolutely. If the day IS sold out, I have heard conflicting answers to that question, depending on the region. Road America is a Mid-West event, so you want to contact Fred Duncan, Brian Blume, or one of the other directors for that region. I know Brian's screen name is "bucky_badger" and I think Fred's just just "fred." They can give you a firm answer.
have fun