Holy crap mate !! I've missed how big this "shed" is going to be but with that foundation spec you could go 3 stories high !!
Currently doing my own build that I thought was over spec'd but this take the biscuit.
Worst part is all the money it takes to get to a finished concrete slab to build from. Reckon I'll be sitting about £10-£12k :-0.
Good luck with the rest of the build - your decidedly doing a grand job !!
Paul