No experience with tarpon but a couple mods I would make to your set up would be the following.
Backing: Make a bimini loop that is about 2' long. Double the loop back against itself and tie a surgeons loop. This will give you a doubled line that will help prevent a girth hitch from forming when attaching to the fly line loop to loop.
Leaders: I would tie your 20lb tippet to the shock using an improved blood knot not the loop to loop you propose. I think this will accomplish two things. More stealth and a lengthened shock. Those loops use up a lot of line in my experience. Put a loop in the 20lb section and loop to loop with your 30lb section. Yes you will eat up more 20lb line over the long run but you will also be changing out the line which is most likely to abrade more often hopefully resulting is less lost fish. I reccomend using RIO or Mason's hard mono for the class tippet. Much more abrasion resistent than traditional mono and easier to knot to the heavy shock.
Leaders: I will defer to the tarpon specialists but the 100lb shock seems heavy for 50-70lb fish. I would think 40-60lb Seaguar fluoro would be sufficient and much easier to knot to 20lb tippet.