What exactly really consitutes as a date?
Well as I was able learn in Eternal Families class, and as have been said from the prophets. There are 3 Ps that really differentiate "dating" and "hanging out".
The first P is Planned. That means when you ask someone on a date you should plan a time and an activity.
The second P is Paid For. This means that if there are any costs on the date, the person who asked the other person should cover these costs. Dates do not have to be expensive, or even cost money though.
The last P is for Paired Off. That means that it is kind of specified that you guys are together on this date. So just doing a game night with friends wouldn't really be a date unless the people on the date are paired off in a way that it is acknowledged who is paired off with who.
What is the purpose of dating?
The purpose of dating goes down to the same purpose of everything else God has created for us. Moses 1:39 says "For behold, this is my work and my glory—to bring to pass the immortality and eternal life of man." We know that dating exists for us to help us become like God. In the end it should be preparing us for marriage to someone we can start a family with and be sealed with.
What is the role of sex in dating?
The law of chastity is pretty clear that we should have no sexual relations prior to marriage. Dating's purpose is really for us to find someone we can grow with. If we date in the way that God intends, we do not worry about whether we are "sexually compatible" with our future spouse as we can trust we will be by dating. Kissing, holding hands, and hugging are definitely appropriate activities to do while dating. Prophets have counselled us teaching that activities such as lying on top of another person, aggressive spooning, oral sex, exposing our private parts to someone else, etc. can violate the intention behind dating. We should avoid such activities.
What is an Appropriate amount of time to date before marriage?
This varies from person to person as everyone has different experiences/situations. I have met people who have gotten married relatively quickly/slowly compared to the average person that are happily married. The decision to marry someone should be based on when both people feel they know the other person well enough to know they want to be with that person forever. One should follow the spirit and seek revelation from God as they look to make that decision.
What if I've broken the law of chastity, Can I still date from an eternal perspective?
Yes of course. In cases where serious repentance is necessary, one should obviously consult with their bishop. But no matter the decisions you've made in the past, dating from an eternal perspective is always a decision that you can choose and should choose to make. What's more important than your sexual past, is your intentions about dating and marriage in the future. Choosing to date from an eternal perspective will always benefit you.