Cheaper for lenses but not the frames. The last pair I brought, I’d question the authenticity, even though they came from a reputable shop, the frames haven’t lasted well. Now I buy frames in Singapore and get the lenses done in Thailand.
both insurance certificates are issued by the insurance company you select, so long as you choose one from the list of recommended suppliers. I’ve just redone my second OA whilst on a trip to Australia, took 7 days. One advantage of living/applying in Sydney is that you one have to show funds in an AUD account not money Thailand. But every consulate can have different interpretations of the rules.
Happened to my wife, no exit stamp at Phuket. Just make sure when you come back you have proof of you original exit flight. They can look up the details and fix the stamp on your return.
Write you own letter, inviting them. I know it sounds crazy but I had to do the same for my wife who is on a trailing spouse Non O visa. It worked with the Sydney consulate