You can apply from home just with income or funds as Lester explains and also in Thailand if your embassy in Bangkok offers to give you a affidavit letter regarding income.
Requirement varies slightly between immigrations. Best to get handed over the requirements in CM before you apply. Reports of only randomly home visits for the retirement extension.
I just use bank to bank transfer myself within maximum a couple of days. Some use Wise as I understand goes quite instantly if that’s an option for you. Not particular expensive.
No you can’t apply for a Non O visa in Savannakhet without proving funds any more and the multiple option is not available, only 90 days Non O based on marriage with single entry which you can apply for a one year extension of at your local immigration in Thailand and apply for multiple re-entry permit to get stamped back within the validity of your stay. The requirement are anyway 400K baht in a Thai bank or 40K baht a month within Thailand. Some immigrations accept affidavit letter regarding income.
You can apply for the initial 90 days Non O visa before you come by proving income min 40K baht a month
You have to update your health insurance to get stamped in for another year. That’s why the IO wanted to see how long your current insurance was valid as you’ll only be stamped back in until it expires. You can update the same health insurance as long as your visa is valid (one year). For the one year extension of stay in Thailand you’ll have to use one of the companies on this list.