You definitely need an ending balance over 500k baht everywhere but some want to see that every month for 3 months or longer. Other consulates stipulate the amount in the local currency which might not equate to 500k exactly
But if you are eligible for a Non-O visa it seems to me the simplest thing for you to do would be to get a 12 month extension of stay each year then you can come and go as much as you please
the DTV has no option for visiting a partner. If you want to get a DTV to apply for one of the soft power activities then decide what activity you want to do then look for an approved provider in the area you want to be
there is no new rule. There is no defined limit for visa exemption entries. The immigration officer you will stand in front of will assess and decide. If you are worried get a visa