Ok, as I see the situation, we are not considering here your current GF as your future wife, she is a history, you have to finish this relationship nicely, that is it. As for another girl, 1. I wouldn't jump into new relationship so soon; 2. I don't think putting conditions by that girl, such as date of engagement and wedding is a good idea, no one should be forced in such decisions; 3. Does she love you in the first place or she just wants to get married?
Your main concern is that you might not meet such girl again, and that's why you should grab her. Well, it is not particularly right way to approach your relationship. Besides other things, Relationship is permanent compromising by both sides, and if one of the sides starts putting conditions without any reason, it doesnt make relationship any healthier.
By the way, have you spent some time with this girl, or it is only long-distance virtual relationship?
I cannot tell you whether to marry her or not to. that would be wrong. But I think if you raise this type of questions, if you are questioning the whole matter, it means you are not ready yet. Take your time, try to explain to her your feelings, and if she loves you, she would definitely agree to wait for a while, without putting any conditions.