wow, what an ordeal... Was just reading this through from the start thinking its gonna be the bottom pulley on the wrong way but you got there without me in the end.. lol
Just for future reference, if you look at that pulley there is a tiny little hole in it that a small pip should slot into so you know you have it the right way... You pip may have snapped off, wouldnt be the first time, but you should be able to tell where is was anyway.
And the starting thing, yes it should require zero pedal to start and Jack has suggested first thing to check. Shame they are getting so rare now, back in the good old days I would have said just pop down a scrap yard and grab a couple of throttle bodies and swap them over but them days seem long gone. That an these mpi P75 engines are even rarer as people steal them to engine swap other little fiats (me included, multiple times, I am infact in middle of sticking that engine in an old 750panda lol)