If i follow the pattern suggested for USA old guys and enter on 30 tourist stamp, get Non-Immig O visa, wait 65 days, then get retirement extension, how soon after that extension stamp can i depart T'land for another country? And how long can i remain outside T'land and be welcomed back without question when i do return?

You can leave the same day you get your extension. Just remember to get a re-entry permit.

You can stay until the day your extension expires. I'd suggest not waiting that long - give yourself a couple of days leeway, at least.

Once you have the extension you will need to apply for a re-entry permit which will be valid until the date your extension ends.A single is 1000 baht and multiple 3800 baht.

You could leave the same day you got the extension if you wanted to and there is no limit on how long you can be out of the country other being back to do your next extension.