Before Thai Smile, Thai Airways operated a few A320 and they all had 8 business class seat. It is quite common to see that in some airlines.
It would be simpler to reconfigure the first row up front with those business class seat and business class passengers would be satisfied.
For this type of documents I always use EMS or DHL.
And DHL need a street address not a PO Box.
DHL is always quicker for me for shipping document in Canada.
Amorn Electric did repair the microwave in myapartment 4 years ago.
They installed a new "magnetron" which is the main part emitting microwave.
I looked inside to see it. So I guess those part are available in Bangkok.
I do not remember the price but it was not that expensive.