multiple countries several months

I will arrive in Hanoi January 8 and be in Vietnam for approximately five weeks. Then I will travel to Siem Reap from Saigon. I will be in Cambodia for one week. After Cambodia I will go to Thailand for a week. After Thailand I will return to Hanoi and travel in Vietnam for at least two weeks. It is possible I may travel to Malaysia for my last week in Southeast Asia. My trip will be from January 8 to March 26.

Can your company help me with all of the visas required? Or do you only prepare the necessary papers for my Vietnam travel. For Vietnam I would want multiple months with multiple entries.

I am an American citizen and have traveled in Thailand and Myanmar last year for two months.