How will my visa work for multiple entries into Thailand with a South African passport?

Greetings all

Getting a bit concerned about my plans and would appreciate some input

I have been to Thailand 3 times since October last year , 10 days and then 21 days twice . Last visit was May/ June

Now I plan to travel at the end of this month with an itinerary of Chiang Mai for a week then fly Bkk to Hanoi spend a week near Sapa , then back to Thailand for a week in Bangkok

How will the visa (s ) work and do you see snags ? I'm on South African passport and flying in and out of Bkk on Emirates . Will have return flight issued and hotel booked in Chiang Mai