One Alien shows work and income from outside Thailand. The spouse can just be housewife or houseman (without the need to proof remote or freelance work) - that is what they probably mean.
Unknown at this time. I personally doubt it. As usually local immigtation offices only deal with financial evidence when it needs to be shown in Thai bank accounts. Not sure how they would handle evaluating financial evidence from around the globe.
I can't say, but I doubt that to be true. People married to a Thai national were never forced into a specific visa. They were free to chose from all visa applicable to them. I don't see why it should be different with the DTV. In fact, I would consider alternatives to the (cumbersome) marriage visa.
Impossible to say for sure. Depends on how many and how recent your previous stamps. Also depends on your port of entry. Both Bangkok airports are known for causing issues. Land borders or other airports not so much. I always chose to be on the safer side and got a tourist visa - which is cheap and simple with the eVisa system, after an unfortunate situation at DMK airport once.
Depends on your local circumstances and the requirements of your closest Thai embassy. For example, in Germany, if you are self-employed, you would register your self-employed activity and could likely use that as proof. Or another thought: Just show your stock portfolio - afterall, they mention a "professional portfolio" as a means of proof. Best to check with the Thai consulate closest to you.
There is no explicit tax exemption with the DTV (unlike with the LTR). After 180 days there may be tax liability. Details of those still not fully clear.