Yes. Cash.

So then you have answered your own question. You say that the process may be complicated and you don't want to book a flight tickets......and that is directly due to the consulate that you have chosen. if you want it to be easy with no need for onward tickets or anything else then go to Vientiane. If you want to go to another consulate, then be prepared to have all the required paperwork ;) Eventually you will have problems with the 30 tourist visa exemption process as they do not allow people to stay long term in Thailand as you you are not a tourist. Good luck.

Go to Vientiane.

Go to Vientiane.

You start getting fined at 15 and up, so it would make sense to get things organized on an ED visa before that. Under 15 I would imagine a lot of kids go to school with no visa and have no problems. Don't have personal experience on the subject however.

Thanks :)

Also as far as I am aware (someone can confirm), under the ages of 18 is exempt from blacklisting. Correct...?

I shouldn't think so, but the gurus will confirm this.

Children under the age of 15 are not charged a fine for overstaying but still get overstay stamps when they leave the country. Not 100% sure of any future issues, but probably none.

There will be no problem.