It's not easy getting good results by trying to save a few Euros.
With XF 56 you are more or less putting yourself back at square one
It's a water based acrylic jar paint. Yes, you can put it OVER Zero paint. YES, you will need to put a clear coat over it. YES, you will need to be careful what clear you use since you would be putting it over the XF56 - I would recommend Mr Top Coat aerosol (Blue can) in that case.
Tamiya also have a TS series Metallic Black IIRC. You could also use this (straight from the can or, as I would suggest, decanted and put through your airbrush for better control).
Whatever you decide - good luck!
