If you're using an international transfer, you can choose what funds to send from your bank. Generally it is better to send native funds and let Thai bank convert. If you are NOT applying for your non-o in-country, the funds do not need to show that they are from a foreign source.
I did it a couple months ago. I used the visa/print service in front of Condochain. They were professional and very easy to do business with. I would not do it on my own.
OA visa is 1yr but cannot be applied for in country. O visa is 3 months + 1yr extensions. Best applied for outside country but can be done in country as well. .OA has insurance requirements as well as criminal background check requirements, O does not. But O has financial requirements. Suggest O and apply through evisa from home country