to 1: nowadays one can stay in the care while filling lpg, same happens with methane (CNG-compressed natural gas), but every european country has is own legislation on it, e.g. in Germany there's afaik only self service and you have to press a security-button for the whole filling process, boring. The adapters are mainly of two types, "dutch (italian) and german".
to 2: The HP's in the car's papers remain the same, for newer vehicles there's a circulation tax reduction for lower pollution. The engine works with lesser noise on LPG and there's only a slight power reduction, with carburettor, with ignition there's none. In Italy you can drive also with smog traffic reduction, even with my old watercooled 26 dogyears old Volkswagen.
Foud a shelter for my egg, yesterday, for free!!
Kind regards, Fabio.