I flew from the USA to Africa at 21 weeks. It is fine but make sure to stand and walk every few hours. You are at a higher risk of getting a blood clot in your legs due to the elevated altitude. I believe there are compression tights you can buy that help circulation.
Yes you should be fine, but clear it by a Dr who knows your medical history
It's normally safe to travel up to 36 weeks HOWEVER I would talk to your doctor first.
Talk to your doctor about your individual health. However, in general, it is safe to travel. Just be sure to get up and walk around the plane every now and then.