for the application to the visa, your original income documents are accepted. However for the application to the 1-year Extension of the Stay Permit in Thailand, you need a certified income affidavit by the German embassy Bangkok over a minimum of equivalent 65,000 THB per month, and Immigration will most probably also wants to see that you have a Thai bank account
yes, it completely changed. Now you need proof of EITHER three months bank statements over a minimum of equivalent 800,000 THB (21.700.- Euro), OR proof of a monthly income of a minimum of 65,000 THB (ca. 1750 Euro)
correct - some people are on short holidays (like oil riggers on leave) however Immigration officers at the borders will still start counting the days. You are absolutely safe if your visa-exempt stays are below 180 days during the recent 365-days period. This is a kind of "rule-of-the-thumb" Immigration is using. There is not one single official rule that limits visa-exempt entries. It's just the number of days spent in Thailand