That way you are seeking two Visa Exempt entries very close together which could be seen as risky or, at least, look bad in the future if seeking another Visa Exempt entry
Better to get your Visa before you travel which makes opening a bank account much easier which you will need soon fter arrival to transfer funds to season for two months for your first 12 month extension.
Your husband's employer will provide the documentation for his Non-B and will need to support your application for your Non-O. You're child's school will provide the documentation for the Non-ED.
If you "just received" your Non-O and you live in Karon then you'll need to exit and re-enter Thailand to activate it to use it to open your bank account