@Mabel ***************
with a "married to a male Thai National visa" there is no 400k baht requirement because it's only for foreign man married to a Thai lady. With this visa you never have to leave Thailand. You apply online in your home country for a non O Visa married to a Thai National. After arrival you can stay 90 days Thailand, time enough to make everything ready for applying for a 12 month extension that you will need to apply for every year.
Your husband can open a business very easily and it depends on what business you want but when you are married to a Thai National you are allowed to "help" your husband behind the scenes without a work permit. Ofcourse if you want to work where everybody can see you then it's better to have some work permit.
The kids will always have a visa because your husband is Thai.