Do a search on the consult requirements and rules. Each seems to do their own thing so best to check what has worked at the location that you will be applying. Are you going with Washington DC or LA?
Depends on the consulate where you apply. If you are in Vietnam, and you apply at the Ho Chi Minh city consulate you can apply for the primary applicants DTV with 500k in a joint account, then after it is approved apply for the spouse DTV using the same financials. At least that is how it worked a few weeks ago when I went through the process. I got my DTV via remote worker/business owner category.