BTW, for the DTV, remote worker (aka digi nomad) and company owner are not considered the same, though they are in the same branch as opposed to the soft power thing. Both are valid options, but in your case you would be remote worker. There are specific places on your application to explain this. If you were applying as company owner, you would need to show proof of your incorporation and give some explanation of what your company does.
IMHO (and it is only an opinion) the soft power part of the visa would be the most likely to be modified if they ever decided to alter the admissibility/ requirements for the DTV. The Thai govt has started to crack down on some "schools" which do not check attendance or document a student's progress... as they realize a lot of it is bogus.
As many things Thai, each embassy/ consulate can interpret things slightly differently.
In choosing where you apply from, consider the responsiveness and speed or processing of the local Thai embassy you decide on. Sometimes a phone call to that embassy/ consulate can be quite helpful to sort out some details.
As a remote worker, you will (very likely) need a letter from your employer stating you are authorized to work remotely from Thailand (yes this specific wording is necessary). If you have had other contracts as a remote worker before, also put all this info in a portfolio/ CV to show you get regular employment. As for the money, 3 consecutive months' bank statements showing you have the required amount 500k thai baht equivalent is all you need.
You certainly do not need a law firm or agent to do this for you, it is relatively simple. When I applied (remote work), the embassy asked me 2 times for more details, which were providing the company registration proof (many countries have official websites where you can check a company's existence) and to change a detail in my portfolio stating something more specifically. Easy peasy.
R.e. doing it "from home country": I don't know about USA but some countries emit an e-visa. So you can try to apply to your own home country's embassy while being out of Thailand (if your home country delivers an e-visa), while visiting somewhere else. Your home country's Thai embassy will not know you are not in your home country, they can only find out if you are or not currently in Thailand (if they do look, cross reference with immigration).