1) The visa gives you permission to stay for 180 days each time you enter. After that you can do a border bounce for a new 180 day stamp or you can apply one time each entry for a 180 day extension. No one knows what the extension entails, how much it will cost, or any other details yet as we are still months away from the first person being able to apply and the immigration offices don't even know anything yet.
2) CAN he partake in courses? It's one of the requirements for a category of DTV. Taking classes has no visa requirement in Thailand. Anyone can take classes regardless of what visa they have.
3) You need to check with the embassy. Each embassy sets their own requirements, and some will require a dependent to show their own proof of funds and some will not.
As you say, that's about the worst place to be for a border bounce because it's not near any land borders that you can use. Why not just go to Bangkok and take a quick flight out and back in the same day? Generally you will want to aim to go to a country that you have visa exempt entry for and don't have to buy a visa on arrival. It depends on your passport which countries that would be.
Otherwise you're in for a very long day stuffed into a mini-bus van as they drive you to a border, get you stamped out and back in, and then drive you back. That's how land border bounce agencies work.