I don't understand what you are asking. E-visa doesn't change anything about applying for a visa except that it's online. You still must apply through the Thai embassy that services where you are physically at. Bob asked a question about applying through the Thai embassy in Phnom Penh while he is physically in Cambodia, which is how you are required to do it. You cannot apply through a US Thai embassy unless you are in the US. When you start the application it asks you where you are at, and if you don't put that you are in the US it will not let you proceed.
There are only 2 borders that are requiring this as of now. Chiang Saen and Chiang Khong, and last report is they are requiring one night in Laos, not 24 hours, not 48 hours, one night.
Yes, both your photo and fingerprints will pull up your previous history. You don't need your old passport unless you have your old long-term extension in it. If not then just your passport should be fine
First you get all the required documents from your company that you need for the extension, and make sure that your work permit is in good standing as well. Then you can go to the immigration office to apply for the extension. Yes, the extension goes into your passport and is based on your working. If for any reason you stop working, then your extension is voided as of that same day.
They won't want to interview you. But if you leave the country and they ask for proof that you are still in the country, they will cancel your application without refund.