I went down the spare wheel route, after a great deal of research and searching, I found that a space saver wheel off the Fiat coupe 20v fits both front and rear of 500, not sure about Brembo break upgrade, but if someone has it, they can borrow my wheel and try it?
The jack came from a Abarth Punto (all parts sourced Ebay/Fiat), what you will also need is some extended wheel bolts to reach through the space saver wheel as the coupe spare has a built in spacer to clear its calipers, thus fitting front and rear 500's. I can measure up the spacer thickness, and also the length of wheel /bolts. (I had to machine the bolts to suit our 500c, the advantage of being an engineer, cannot remember sizes as did this 3 years ago)
What you will need though, is to change the Tyre to a 125/70 r16 on the coupe wheel it was a 125/80 r16 tyre on the wheel I sourced. (The tyre was the most expensive item at about £80 if I remember correctly.)
The tyre needs changing to give the correct rolling diameter or as near as you can get.
The jack, I modified the nut so that it cleared the skirts, and you then you can get a socket on the jack and reduce the risk of catching your paint work.
I can take some pictures and post if people wish?
Hope this is of interest and helpful.