I am struggling to find consistent information on visas and hope you can help. I am doing the China Odyssey tour, arriving Hong Kong on 19 Sept and when it ends on 13th Oct, I will be flying from Shanghai to Hanoi and travelling within Vietnam, then flying from Ho Chi Minh City to Siem Reap in Cambodia and eventually returning from Phnom Penh via Bangkok on 28 Oct.
Am I able to get visas for the three countries in advance? How far in advance is possible? For example, the Foreign Office guidance for Cambodia suggests it is more common to obtain a Cambodian visa on arrival. I would rather sort visas myself than pay a lot of money for a visa service.
Also, does it matter that I will be entering Vietnam from China, or Cambodia from Vietnam?