You should check with your local immigration office to confirm they will accept the combination option. If not sure about what they will accept it it would be best to meet the normal requirements by having 800k baht in the bank for 2 months
Too use the combination option you would need to have 400k baht (first extension only and then 200k baht for the next one)t in the bank and proof of transfers of at least 50k baht for 12 months. You do not need to keep the 50k baht transfers in the bank.