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.
Not really. You can draw up some documents yourself and as long as someone is paying you and you have the 500,000 in the bank you've got a viable business as far as the consulate is concerned.