5) this should be localized
4) no need for getting item list, you can buy straight away, It's up to you when you want to call consume (if at all)
2) usually after you trigger some action, please do some code and then you'll see. REFUND is not yet supported

In general you should read Google Play and Apple Store docs about the purchases, I'm new to it as well.

I have read it, but of course we can't look into what your code is doing. It's bit strange to ask your customers to "do some code and then see", which practically means guessing what the code does. :-)

The Native stores send you those messages, I just pass them through.