What are the requirements for getting an ED Visa? And how many hours per week must I be in class?

Getting the correct information from language schools is impossible. I want to get an ED Visa, but I want to do it legally, i.e. Not with the language school falsifying my paperwork.

You must be enrolled in a 400 hour course of study. You must attend classes 2 hours a day 4 days a week.

Note that you can study Thai on tourist visas, and many people find it easier just to do that. It does mean visa runs every two to three months, but from a paperwork viewpoint is simpler.

52 minutes ago, soistalker said:

I want to get an ED Visa, but I want to do it legally,

You will start by getting a 90-day single-entry ED visa from a nearby consulate (or in your home country), which will require extensions to complete a year.  The process for these extensions varies somewhat, depending on the the immigration-office that serves your area.

Even if you do things "by the book" - attend classes and study - you may still wish to ensure the school you choose can facilitate your extensions for an additional fee.  This is to ensure that you get full 90-day extensions, versus short 30 or 60 day extensions and/or other harassment.  This system appears to work similarly to the way agents are used to assist with other types of extensions, regardless of the underlying qualifications.