Given the alternatives - a night spent in a 400-500 baht equivalent Guesthouse - seems okay

Still can be done - just have to stay longer.

Yes as Tod said -(expanded a bit for your locale) go to Krabi Town immigration office - extend for 30 days - then when that 30 days is running out - take a hired taxi or rent car or border run van to Thale Ban National park border checkpoint in Satun Province (not far from Koh Lanta). Do an out and back in at the Malaysian Border - get 30 days. Then extend that 30 days.

With the right software the PDF form can be converted to on screen data entry

Go to Vientiane, Laos to the Thai Embassy / Consulate there. Fly direct from Bkk. Or fly to Udon Thani and then take a bus. No company needed.

Yes

Not really any agents in Vientiane - signs discourage it.

25 kilometres

Under certain circumstances, Condo investors can get an Elite Card in the deal - good for 5 year.

Non O is not just for Marriage. The Non O can also be Extended for One Year based on being age 50 or over (retired).