Finding files with the same info in them

I have a large number of files stored in a specific directory, there are 3 fields in these files that I need to do a few things with

These are the 3 fields in each file

Subject:

From:

HelloName:

I am trying to find out how many of these files have the same "Subject:" line (i.e. everything after the : in subject is the same)

List out the top 3 Subject (top 3 being the most number with the same subject line)

Pull out the From and HelloName from those files and put it in to seperate text files.

so far i am using the below, however I am at a lost on how to group and count these to determine which are the same for grouping and the count

select-string *.txt -pattern "From:' -list

any and all help is appreciated