Advice for a newbie? Don't show all your cards and have exit strategies. Have a plan just in case your job is not as promised. Some backup plans you should have are:
- Know where to go for temporary accommodation
- Know how to find your next job
- Know your visa rules
- Have enough cash to last you 2 months without work
The above list should cover you. Don't by any means, pay an up-front fee though. Some schools are just waiting to use and abuse you for their own benefit.
Haven't heard anything bad about OkayKorea. Most I know about them is that they are a recruiting company. Just ensure that they don't dock your wages. The school they place you in should be paying them, not you paying them indirectly via lower wages.