Air ticket booking can be made by travel agent, but also it can be made from HP of each air plane company.
Fasting period and in September and around the holidays, the price tend to be expensive. But there are so many LCC, so it's better to check them.
When you come to Indonesia as a tourist, you will be required to obtain short-term tourist visa. You can buy it on arrival at the airport. It takes 25 dollars for stays of 30 days, can be extended up to additinonal 30 days.
Before leaving your country, validity of your passport should remain more than six monthsm and there should be three pages or more blank pages about your visa.