Working Visa

No such thing as a working visa.
The employer should apply for a work permit then, on successful approval, apply for a KITAS.
All costs are the responsibility of your employer, and not passed on to you.
Luke should be able to provide the details as he's far more familiar with that area than I am.

All you need to show to immigration on arrival is your passport. You new employer should tell you what you need to when arriving into Indonesia and you should ask if they haven't.
Hopefully for you this is a discussion already had.

However having a return ticket to show is useful if asked but this would normally be done at your airport of departure. If your Visa is in process then you may need to buy the 30 day Visa on Arrival rather than the free one but again do ask your employer.

If you have already got the kitas then you should just show the information to an immigration officer who will help to the right desk for stamps.

Share your concerms with your new employer because they should help you with information like this because airports all handle foreigners slightly different here.

Many thanks for the info Fred