Do I need to take my Thai wife to apply for an in-country Non-O visa and how does the fund requirement work for extensions?

the O/P uses Chaengwattana bangkok so I think at this point they have enough info and can get their initial non-O visa applied for here in the near future

You have not mentioned which office you will use. Some require 2 months seasoning for the NON O. Pattaya is one, as an example. Check first at the office you will use to make sure.

Q. * Do I need to take the wife for that, or only when I apply afterwards for the extension part?

-> You must bring your wife when applying for an in-country Non-O visa and a following 1-year extension.

You always bring "the reason" for your visa or extension, in your case, it's your wife.

Q. *How does it work, season for two months prior to the extension? After you receive the extension you can spend down, but must top back up to the 400k baht the following extension?

- Generally, no minimum period of your funds of 400K baht to stay in your account for the initial in-country visa. 2 months of seasoning on the day of application is required for only a 1-year extension but for every time.