Yes, you should be able to feel a disc like hardness under the nipple/arreola. Do you remember this feeling pre finasteride? I still remember feeling the disc during puberty(very common for boys to have some form of gyno during puberty) but had no idea at the time what it was. Thank god it went away.
It does appear you have mild gynecomastia, however sometimes it's really hard to tell. Mine was easy to tell as I could only feel the round disc on one side of my chest. Good that you're going to work out as it may be so mild that if you drop down to a low bodyfat, it won't be noticeable.
If you've always had fatty nipples similar to your pictures, then you may have already had mild Gyno before taking finasteride. Your pictures 1 and 2 doesn't seem like it, but pictures 3 and 4 does seem like mild Gyno.
I believe your surgeon also came to that conclusion from your update.