Good for you for wanting to answer this question for yourself. It really will make your relationship with your bf so much better.
I’ve been dating a wonderful Catholic man for the last 2 years (and are close to engagement), and I can tell you what “rules” we go by. However, I’d highly suggest you read “Good News About Sex and Marriage” by Christopher West. It will answer all those questions for you!
First, we don’t do passionate kissing, it just really isn’t a good idea to do that because it can lead to too much arousal or making out. We do kiss, but it is still a chaste (ie: closed mouth) kiss.
Second, we don’t do anything that might cause temptation such laying down together, spending the night in the same place (alone) together, watching any really drawn out love scenes in movies (shouldn’t do this anyways), etc.
So in regards to having questions about intimacy, I’d say it is fine to talk about some things…however specifics really should be saved for engagement and when you are closer to marriage (plus you can clarify with your spiritual counselor helping you to prepare for marriage). My bf and I have talked about some things such as NFP and morality of things in the act (like what is permissable and not).
I think reading the Christopher West book together might not be a bad idea. The chapter about Chastity in Marriage might get a little more explicit than you need to be now, but it would probably answer some of the questions you have.
Also, this link is also intended for marriage, but it could be something you could both read on your own and talk about more closer to your marriage. I think it has some good points even if it is a little more detailed: marysremnant.org/News/Archives/MaritalSexuality.html
I’m so glad to see someone else wants to remain chaste before marriage!!! God Bless you!!!