It looks genuine to me, including the Grille sans fin cancel. Congratulations!
Given the age and the condition of the stamp, I would not recommend trying to remove the backing. Learn to live with it. You may end up exposing a major thin or repair.
Personally, I don't think it is necessary nor economical to get it expertized. The only forgeries you really have to watch out for are the Fournier, Spiro, and Sperati forgeries. I don't think any of them used that type of forged cancel, but you would have to check the forgery compilations. Also, there should be 97 pearls in the circle.
It's a nice stamp, but realistically, it has 1 1/2 margins at best, and is missing a corner. On premium imperforate stamps, there tends to be a huge drop-off if there are not 4 clear margins. To put it into perspective, my #2 with 3 full margins and no other faults was purchased for well under $100 about 5 years ago. That's what I mean when I say it may not be economical. I didn't get mine expertized. I just put it into my album and enjoyed it. I think you would enjoy it more that way as well -- but that's just my opinion.
Thanks for posting the pic! Great stamp to have!