What is the best route for a SEA trip?

I have 10 weeks around. I’m going to Bangkok this Friday. I want to visit the north and south of Thailand. I don’t know what I’ll do after that. I want to visit Cambodia, Vietnam or Bali and Malaysia. What kind of itinerary should I follow for my trip?

For example: Thai(north) -> Thai(south) -> Malaysia -> Cambodia -> Vietnam -> back to Europe