My question is, how successful are these relationships that end up with marriage? What kinds of things can we do to ensure the success of the marriage?
My situation isn't EXACTLY like yours, but it is similar.
I met my husband in person, and we managed to see each other every month or so once we were engaged. Apart from that our relationship was long distance until we got married. He was in his hometown with his family, working and going to school, and I was 400 miles away getting my education.
Like you, we spent a lot of time talking on the phone, texting, messaging, etc. We emailed and talked every day. Now, you can use skype to actually see one another while talking. Skype is great, we use it to keep DD in touch with her grandparents and aunts/uncles. We also did 'movie nights' over the phone. We'd put in the same movie, press play at the same time and watch it with each other on the phone so we could talk while watching the same thing - kinda silly but it was a fun 'date' for us.
So despite being separated for all our courtship, so far we've had a successful, happy, loving marriage. Going on about 5 1/2 years.
What helped is that we have very similar desires, goals and dreams for our life. We were able to talk honestly and openly through our courtship about our feelings on marriage, religion, child rearing, finances, etc. and had a willingness to negotiate when our ideas didn't quite match up.
We also made an effort to see one another in person as much as we could. We managed it every 4-6 weeks.
A key thing, as well, and something I'd suggest to you, is when you do meet her, ask to meet her family. See how she interacts with them. She how they interact with her. That can tell you a lot about her personality.
So to answer your question: long distance relationships CAN be successful, if you have two people communicating openly and honestly about who they are, who they've been and what they want for the future, and if those two people have the willingness and ability to resolve their conflicts.
When you think you're getting to the proposing stage, I'd consider sharing the Marriage Builder concepts with her and see what she thinks of them. Until then, I'd try to spend as much time with her as possible, getting to know her and letting her get to know you.