Osaka/Kyoto

Hi!
I'm from Malaysia. This is my first trip to Japan and was hoping to catch the cherry blossom in Osaka/Kyoto. Below is the tentative itinerary :

3/4/15 arrived Kansai Airport - Otsu ( I couldn't get a hotel in Kyoto, so I settled for a hotel in Otsu)
3-4/4/15 - Kyoto
5-8/4/15 - Osaka
9/4/15 - depart via Kansai Airport

My question is :-
1. Do I still need to purchase The train ticket while back in my country or I can make my purchase once I arrive Japan since I will only traveling around Osaka/Kyoto and vicinity.

1. What is the best transportation mode and cheapest?

Thks.