I believe the SUICA card is for JR rail where is the MetroCard is for the Metro around Tokyo. Anyway you can buy it at the ATM machines when you get here no rush
Line is a messaging application that's very popular in Japan. So when you meet people you will want to be able to talk to them via line.
You might want to load up the hello talk application. And meet some people in the places you're going to visit have some conversations with them and then when you're in town you'll have a local that you can bounce ideas off of and perhaps making sure you around a little bit.