Roughly, depends on the max output of your panel and the hours of sunshine you get. remember we have a rainy season. And I am just as puzzled as you probably are by the huge price differences between the various brands, etc...
It is what is needed, depending on the performance of your panels (2 KWh a day might be seen as conservative by some) and the amount of sunshine you get, if you want to be off grid i.e run off battery at night.
I don't know about that, but they quoted me 2.2 THB, but reluctantly yes. Some guys here boasted that they run their meters backwards, but that's illegal and PEA is in process of changing their gear.