Hello and thank you for the question.
We have written a lot about healthy boundaries in a relationship in the past. See for example "Where should my boyfriend and I set boundaries?"
Daring to talk to your partner about setting boundaries is always important. Then you can "ventilate" feelings, thoughts, insecurities and questions. At the same time, it is easier to stay within the limits that have been set if you have said it out loud and agreed on it. There is a lot of freedom in knowing where the boundaries are.
You ask about legalism, that which is good in the sight of God. The two things are not really opposed to each other in this question. It may sound like you think some boundaries are legalistic, while others are healthy. Borders in themselves are not legal. Even those that are much stricter than what we ourselves want to recommend. Like for example. not to give each other a hug or not be alone together in a room. Some people want these limits, and experience them as healthy and good. But in themselves they are not legalistic.
Lawfulness is mainly about our image of God and whether we believe we can earn grace by doing or not doing certain things. And in its ultimate consequence, legalism is the idea that we can make ourselves righteous before God. We can't do that. Only Jesus can do that. And Jesus dealt with this way of thinking when he spoke to the Pharisees and scribes. Choosing certain frameworks for a relationship is not necessarily legalism, even if you think it may be strict. But if you believe that God's love and grace for you depends on these frameworks then it is legal.
Boundaries are important, because it's about respecting yourself and the other person. It's not just about waiting to have sex until you're married, but about protecting your emotional life.
You are not specifically asking about sex, but we encourage you to think through your definition of sex. We believe that sex should have a broader definition than some people set today.
Read more about waiting to have sex until you are married: "Ten Good Reasons to Wait With Sex".
Good luck with your relationship, engagement and marriage. Remember to use the time together well. Each stage has its own joys and challenges. There can be a lot of joy in waiting.
Kind regards, boyandgirl.info