Can someone correct me if I'm wrong

If I get a multi entry visa

1. valid for 6mths

2. has to be used within first 3 months.after issue

3. X number multi entry's stamped in for 60days at a time

4 if I do last entry say 5mths 3 weeks before visa runs out do I get stamped in for another 60days which will take me over 6mths mark

5 .What I'm not sure of if one of the 60 days can be extend at immigration for another 30days 90 in total

Would this affect any remaing time left on visa

Might seem like a daft question, I have a 6 month multi entry visa, got stamped in for 60 days a few weeks ago, but have decided to head to Cambodia for ten days or so then come back, is there anything I should be doing at airport visa wise before I leave or simply show them my multi entry when I get back and get stamped in for 60 days again? Thanks

I live in Spain as a Danish citizen. For practical reasons I am going to apply for the multi entry visa in person at the Thai embassy in Denmark, on december 27. It normally takes 3 office days. My flight to BKK is booked for january 7. It should all be fine.

However, if it fails for any reason, will it still he possible to apply for the multi entry visa when arriving in the airport?