The Bible suggests that two people should walk in agreement (Amos 3:3). In any relationship, it is important that both people can walk in agreement on perspectives. It is particularly important to have the ability to walk in agreement if you are getting married. I do understand that even when a Christian is dating another Christian, they may differ in their level of knowledge of God, and have different opinions on some topics. Thus, it is important to discuss your views on God and other topics as well. It is important that you make this mental connection with your mate; it is even more important than your sexual attraction towards your mate. If you are a Christian dating and leaning towards marriage, I believe that God's salvation is an important quality in a mate. Don't throw stones at me when I say this, but, even if your mate is a Christian, your relationship will still take much work. You both must communicate with each other and learn how to walk in agreement with your mate (which may require a compromise on both sides). It is unfortunate that many Christians are getting divorces because they were unwilling to communicate and/or compromise in order to work through their issues. You must learn each other's perspectives on God and life. Also, you both must be dedicated on working through issues and learning how to walk in agreement before you move towards the wedding chapel.

To this question, I give a strong NO.  If you are a Christian who is dating someone who is backsliding from the faith, that person may become an anchor that will bring down his/her mate.  The two of you may be moving at different speeds (of being in a committed relationship, and of understanding God), but it is important that you two are moving in the same direction (i.e. you both do want to be in a committed relationship with each other, and you both share similar values of having faith in God).  You can't be going in two different directions and expect God to bless your relationship.  

After about 9 months you should have talked about your perspectives on marriage.  If you do get engaged, I believe the engagement process should not last longer than two years.  After two years, usually the man will get lazy with coming up with a clear marriage date, leaving his future wife in an uncomfortable quagmire.  This obviously is not a good start to a marriage that is supposed to last a lifetime.