I don't think For Each and Blast SOP are very suitable for this. The reason is that in a dictionary elements are accessed by key, not by index, so getting the length of the dictionary will not help much in the end. To make this possible For Each SOP needs to be able to iterate over keys and not over indexes, but this feature is not available here.
If you really need to iterate through the dictionary and look up or delete something, then use AttribWrangle.