Samsung Galaxy S2 working in Japan?

So I have a Samsung Galaxy S2 (Model SGH-T989 from Tmobile). I'm running Android 4.1.2 (Jelly Bean). It is also unlocked. I will be taking it with me to Japan, and I am intending to stay there for almost a year. I was wondering if anyone had any experience with this phone abroad, and could help me out. We recently switched to a business plan, which also has free data abroad, but I'm not quite sure I want to rely on that. I think I will be basically needing just data (I use Line even here in America). I've heard of many types of sim cards and plans abroad, but what do you think would work best taking this particular phone into consideration? Also, I've heard of people having problems accessing the android market/play store abroad. Would it be best to root my phone before going to Japan? I'm not sure if that would help or not. Also are there any apps that are a must have?

Please be advised that the thing is not whether it works in Japan or not, you must check out if your device has a 'Giteki Mark', which is printed on devices such as smart phone approved by Japan government as a legal one to be used in Japan.