Operation and development of APIs are currently fully funded by company Apitalks and its usage is for free.
Yes, you can.
All important information such as time of last update, license and other information are in response of each API call.
In case of major update that would not be compatible with previous version of API, we keep for 30 days both versions so you will have enough time to transfer to new version. We will inform you about the changes in advance by e-mail.