Yes he is a coward with a Mickey Mouse title. He ran away twice now. He is a fraud who picks his battles carefully.
Yes he knows Shanks and his crew wouldn't kill him. Easy to be brave when you know someone will spare you. Contrast this to MF where he didn't go near WB, Marco or Jozu. He stayed in his weak ass lane fighting fodder and Vista.
Yes he is excited that he has to run. This coward motif will be expanded where he gets chased all over the Grandline until he asks Shanks to shelter him under his protection.
Zoro will never surpass Shanks. Being PK is far harder than WSS and Shanks is closest to the throne atm.