No... then it's not Non-O "based on retirement" anymore, then it's Non-O "based on marriage". Different kind of visa, different requirements. For a "retirement" you will always need the 800k or the 65k/month.
It's not really a rule... it's more like "up to the discretion of the immigration officer". It might depend on your entry history what he decide. Since you have a valid visa you should be fine with same day out/in, but... there's no guarantee for that.
An agent can clearly help with the paperwork if you fulfill all the requirements. Some agents can also help to "close the gaps". But... that's not really a good way.