I once went under 800k by 49 BAHT for a few MINUTES and had to start the process from new which included a new visa from Malaysia. Very expensive mistake.
Not until I questioned several times did my local office admit it is 2 months prior, even though they had given me an out dated hand-out the first time I questioned it, so be prepared.
Fortunately for you they seem strict on the 800k baht minimum as I once had to do a visa-run and start again over 49 baht shortfall for a couple of minutes !
Be aware at least one Immigration Office (Sukhothai) will not allow computer-filled paperwork. I have a dislocated shoulder with a broken humerus bone and they still won't allow any fully printed forms. My girlfriend has to WRITE it in for me and then I sign it.
Remans, the word "retirement" refers to the word "work" only. They are opposites and, under no circumstances, cannot be applied at the same time. They are MUTUALLY EXCLUSIVE so no, you cannot work (own business or not) at the same time.