Residency is no longer required to apply in Japan. I recommend making use of the pre DTV application service, Tokyo Embassy offers to ensure a successful application. A couple of recent applicants were given 6 month METVs instead of the DTV.
It is probably better to apply as a remote worker if you can. There is no minimum income requirement. I was similar to you, I only had one contract I could apply with that qualified for the DTV but it was very limited income. All the embassies I contacted told me to apply regardless of income. I got mine via Taipei which is among the stricter embassies. 2m THB savings will be a big plus.