I recommend going there in advance and ask for their latest handout of requirements. Every office in the country differs and every office changes subtly from time to time.
the correct phrase is RETURN OR ONWARD flight. It doesn't have to show you return to your home country - it does have to show that you will leave Thailand.
no - but I have consulted several. My own family doctor, my partner's consultant and a family friend (who is also a consultant). Plus - I listen to medical professionals over and above conspiracy theorists.