That is totally correct stamp. Info in the VISA CLASS field says "Non-RE", which means you entered on a Re-entry permit with a Non-Immigrant visa/extension, in your case with Non-ED based extension.
Or, ask your employer to prepare enough documents to apply for Non-B at the embassy/consulate outside Thailand (which embassy is according to the employer's direction).
You need to have more than 15 days minimum (more at some offices) remaining with the tourism entry stamp for you to be able to apply for an in-country initial Non-B visa.
Burmese on a 14-day entry stamp can apply for a 30-day extension, but it's not for tourism purposes, it's based on the Embassy's request.
I have never heard someone can apply for an in-country visa with an extension based on an embassy request (except special cases during the early stage of Covid chaos), you need to check with the local immigration office whether it's possible.
Check with your local immigration office for their detailed requirements, but there is no general rule on funds being transferred on the same day every month.
Some offices require you to transfer 65K at once per month, most offices accept monthly transfers "total" of 65K baht, like you said "35K + 10K + 20K.
If you can provide 12 times of monthly transfers of 65K baht as your local office requirements, you can switch.
Thank you for the report. So Phetchabun office is another one that requires 2 months of seasoned funds for an in-country initial Non-O visa based on retirement.
Yes, some reports say that property visits or interviews were required for the initial visa based on retirement at some offices.
Your accommodation could be under your partner's name. As landlord's documents are required as well at some offices.
A 30-day tourism extension is added (top-up[) to your tourist or visa-exempt entry, not starting from the day of application. You don't "lose" any day of your tourism extension by applying earlier.