Questions on taxation of an individual and on registration and accounting of BV

Good day. Based on the results of a telephone conversation on Monday with employees of your company, they came to the conclusion that the questions should be formulated in writing :).
1. Property tax for individuals. Initial data: residential building, average cost 1,2 million (WOZ from 2015 to 2018 = from 1,112 to 1,327 million), non-resident owners - only box 3 (sometimes one general declaration was submitted, sometimes two for husband and wife, simply dividing all amounts at 2), mortgage 107520, monthly mortgage payments are now 161,28. Question: how will the tax amount change if one of the owners becomes a resident on a business or study visa, like a Kennismigrant (if there is a difference)?
2. It is necessary to change the address for receiving correspondence from Belasting to the address of the house in Holland, now everything is sent to Moscow, letters are lost or arrive too late - fines constantly arise. Now the student daughter lives in the house, there is the possibility of prompt access to information. Can you do it? Price? Deadlines?
3. How can a non-resident independently fill out a declaration on the Belasting website (there is no DigiD number; only box 3 from income)? If the answer is “no”, then do you provide such services to individuals? Price? Deadlines? For what years can you do it now? – For some reason, previous accountants did this with great delay.
4. Do you provide WOZ reduction services? How real is it? How long does it last? Price? Timing?
5. How much does it cost to register a BV with founders only from Russia or with a founder both from Russia and from Holland? What exactly is included? Timing?
6. What is your BV service cost? If there is a difference in value due to the volume of documents, turnover, etc., including zero declarations, please let us know all the options.