I can't find anything in the DC leaks showing any Soros control over the Five Star Movement (unlike Podemos & Syriza which are his toys).
As far as I know the Five Star Movement is fully independent and self funded (by members) and on their blog there's several articles attacking Soros:
http://www.ilblogdellestelle.it/lo_squalo_george_soros_dietro_le_proteste_anti_trump.html
and they also have a soft stance on Russia (which won't please Soros)
http://www.beppegrillo.it/2015/12/stop_sanzioni_alla_russia_e_rimborsatelepmi.html
Grillo does agree with Stiglitz on monetary policy but that's about it.
the 5 Star Movement is similar to the Pirate and Internet party, with an online platform for participatory democracy where members can propose, discuss,and vote laws and policies. they are a godsend for Italy IMO, though Italy might collapse before they even gain power for the reasons you mentioned.