I just like to declare variables to remind me what is in a macro. I also like to put a really unlikely value in something that is going to be calculated so I can tell when it has been changed in the macro. If you write a long macro you do not really want to search for the point at which you first set a variable to some value so it is better to list them all together at the beginning but it is not a necessity. You can also add comments to the line with the declaration in if you want that reminds you later, maybe a year later for example, of what that variable is for.
The order of probing is a personal choice and depends on what you are doing. As I don't have a full understanding of what you are doing I just chose a general probing order.
