18th is Sunday. The immigration office isn't open on the weekends. So you better go on the 16th. I was supposed to go in on the 18th too but then discovered it was a Sunday. Now I'm going to be two days over on my stay. Lol..
Good luck man, you need way too much shit plus you have to have a lot of money in a Thai bank. Plus proof of monthly income. I would love to move to Thailand but they don't want foreigners here unless they have lots of money.