So they're still allowing the use of paper forms? That's good. Hope they will allow them indefinitely. For land borders, I presume paper forms will remain the default option but they'll probably ask you if you've filled out the form already in advance.
Thai immigration uses helpers from the neighboring country, especially at the Cambodian and Burmese borders, so you'll be dealing with Cambodian/Burmese nationals wearing immigration shirts. They speak far better English than the Thais, one of the reason they're employed not to mention they are also used to help their nationals who may not speak Thai or English [or not well].
Yes but if arriving by land there probably won't be any machines available. Some land borders have only temporary facilities so you'd need to fill out the form on your device at the latest when you arrive before passing through the border or preferably the morning you depart your hotel in Laos, Cambodia, Malaysia or wherever.
You were lucky there were so few people. That border can get busy with Cambodian workers. Thais are rare except for casino punters as Thais don't like Cambodia so it's always Cambodians who are in the vast majority of those crossing the border.
Not at land borders though. These kiosks will probably only be available at airports. Thus for land arrivals, complete your card at your hotel before heading to the border or if you must, on your laptop or phone while at the border.
I asked about kiosks at land borders when I reentered Thailand by car the other day. The officer told me he has no idea but doesn't look like it. Most likely you'll need to use your laptop or smartphone to fill it out or borrow one. Best advice if traveling by land is to fill it out on your laptop while at your hotel the day you cross back to Thailand.