First of all, give up on any idea of extending the DTV. It's almost impossible and even if you do manage to do it, you'll have to take so many trips to immigration and spend so much time in the attempt, that you won't even bother next time.
Just do a border bounce when you need more days. You're not required to spend any amount of time out of the country. You can cross a land border, turn around, and re-enter immediately for a new 180 day stamp. You can fly back same day if you can find a flight schedule that works.
Immediately travel to the country where the application was submitted and hope they don't discover it or they'll cancel the application with no refund.
No one can say for sure. But it's more about the total time in Thailand than it is about number of entries. Generally people start running into issues once they've been in Thailand for 90 days in a 6 month period, and 6 months within a 12 month period.
they're not, because they can all mean different things legally, and different countries view them differently as well. For example Thailand does not recognize civil unions or any other type of partnership besides full marriage.