Inordinately Brief Responses to Really Great Questions
1. What is going on when baptism is affirmed?
Nothing, and everything. From a theological/historical perspective, it's a vestigial structure left over from the bishop arriving to bring the Holy Spirit post-baptism. But nobody knows that anymore, so it's a cultural institution valued very highly by most Lutherans and others because they did it as youth, it's the time to "get religion" or "do religion." So, although it doesn't have the sacramental character of baptism or the Lord's Supper, it ends up being given as much cultural and existential weight and freight, maybe even more so.
I don't think it is using baptism, because it is something to be undergone rather than something in which to find comfort and hope. That provides a concise answer to #2.
2. Is this the same as what Luther means when he talks about using baptism?
3. What is the propriety of the language of covenant in baptism?
I use this phrase in my baptismal instruction which may or may not be helpful, but I use it anyway. "In the life of the child, baptism is all grace. In the life of the parents, the baptismal rite is all law." This isn't strictly true, because the parents receive the consolation of their child receiving a means of grace, but the actual rite is very law and instruction oriented for the parents. Infants baptized in this rite receive pure gift. So if there is a covenant, it is a divided or split covenant, as in "I, the Lord, do everything for this child in a completely free manner, but you, the parents, promise to do thus and so."
4. In the LBW baptismal rite, the baptized, sponsers, congregation, and parents make promises. How do we understand these promises theologically? Martin Bucer introduced them as a prefatory rite/preparation for baptism so that he could understand infant baptism as baptism conditional on these promises. Where should these be and what do they do?
In their best form they create a context in which the child will be raised in the faith, "asset building" that includes the whole congregation. Liturgically, I think they should be after the actual baptism in the name of Father, Son, and Holy Spirit, and in a true liturgical sense, they should be liturgized in the daily, weekly, and monthly life of the congregation.
5. How many rites of baptism include a prayer for the blessing of the water? Does Luther's flood prayer do this? What function does this prayer have?
No idea on the first question. I'm not convinced that Luther's flood prayer blesses. It certainly "remembers", and invokes heilsgeschichte. In my baptismal instruction, again, I believe the function of the prayer is to remind all of us praying of the context "in which" the infant is baptized. This same God did this same thing with this element, water, in many and various places, and now does it here in this place, for you.