Katia,
Even though I don't come from a Christian worldview at the moment, I found myself dealing with many of the same issues you expressed in your post prior to our first IVF. We were fortunate enough to be able to afford to freeze our left over embryos, however, they did not survive the freezing process. I grieved as though my baby had died. The only comfort I had was that we had done all we could to give them a chance at life.
A couple of things to consider before deciding to freeze or not:
1. Our clinic will not freeze day three embryos, only blastocysts, as they have found that they have a 90% thaw rate with blasts, and about a 60% pg rate with blast transfers. However, it does cut down on, or in some cases eliminate, the number of embryos available for freezing. You could very well have eight embryos, transfer two, and have none of the remaining embryos make it to blastocyst stage.
2. With male factor IF, your fertilization rate will likely be lower than average, so it is also a distinct possibility you will have none left to freeze (this was true for us on three of our four attempts)
3. While freezing is expensive, technology has advanced to the point that it is nearly as successful, and far
less expensive, to do a frozen cycle over a fresh one. I think our frozen cycle would have run $3500, not counting the $800 freezing fee.
4. Does your clinic have an option (ours did) for donation to another infertile couple? This would be one way, if you are comfortable with it, to ensure that your embies get a chance at life.
Ok, those are my thoughts re: leftover embryos.
With regard to your thoughts that perhaps you are being selfish wanting to experience pg and childbirth. I don't think so at all. I believe we are created to want and need to procreate, to ensure the contination of our species. So, the desire to create, bear, and birth children is a basic, primal need that is programmed into our very beings. I don't believe a woman wanting to experience childbearing is any more selfish than one wanting to experience food and shelter. To me, it is that basic. On the other hand, I know plenty of women for whom the need has never manifested, just as there are some people who are happier living a nomadic life outside of conventional housing. To each her own, but if the need is there, I don't think it can be denied. And if you do decide to adopt, mourning the loss of the childbearing experience is, IMO also very normal.
A final thought, as this is getting very long. There was a book I read when I was going through the same feelings/emotions you are dealing with. It is called "When Empty Arms Become a Heavy Burden." It is actually written by a Christian woman and comes from that point of view, so it might be particularly helpful for you. I found it comforting for the wisdom I was able to take from it, even though it came from a different viewpoint than my own experience.

All the best to you. This is a tough road, and so unfair, but having come out the other side, I can say it is worth every step.