I loved my time in Korea. I wouldn't trade it for anything. Every hagwon (private school) in Korea has its issues and obviously there will be cultural differences since, chances are, you're a round-eyed westerner that dropped yourself in South Korea. This school, SLP (the wangsimni branch) was really good. I've heard some horror stories about evil head teachers or no exact pay day or basement apartments with roaches as roommates. But SLP took good care of me. The apartment was nice, tiny, but it was just me living there. Made cleaning day super easy. It's in a middle class area of the city so it was safer than most American cities. Far enough from the drunken bar fights scene, but close enough to a main line of Seoul's amazing subway so that if the bar/club scene is your thing, you're just a few stops away. If you're a sight seeing, shopping nerd like me, you're just a few stops away from some serious markets and malls. And book stores, with English sections, too. There was also an amazing Korean language school nearby too, should you feel the need to learn some of the Korean language so it doesn't all sound like gibberish to you anymore.
SLP's Korean teachers were pretty helpful too when it came to making appointments or giving us foreign teachers directions or advice on where to go for whatever it is you may need. Not to mention, the head teacher takes you out for lunch after you arrive for a welcome/get-to-know-you meal. Also, in the building that the preschool is (at this SLP, it's preschool classes in the morning and elementary in the afternoon and then the USA equivalent of middle school in the evening if you're an afternoon teacher) there is a supermarket on the first floor and a doctor's office on the third floor (an English speaking doctor who doesn't charge SLP teachers for visits) and a pharmacy on the first floor. Convenient when, in that first month, you get weird colds while adjusting to the new environment.
Seoul is a relatively open and worldly city, but you will still find some people who are wary of the wei-gooks (foreigners) who are roaming the streets. But you'll meet good and bad people everywhere in the world. For the most part, if you appear to be open and show a desire to 'fit/blend in' (if that's possible) and don't yell at the locals in English, the natives will be as helpful as they can to you. Even if it means doing a little miming or just dragging you by the arm to show you what it is you were asking about.
Vacations are nice. Ten days in the summer and ten days in the winter. Perfect travel time (I went to China for summer vacation) and just enough time in the winter to go home to have Christmas with the family if you want to (I did).
You will have no trouble - with a little leg work - finding anything you could get at home in Seoul. Here's a couple of tips though. Deodorant is nonexistent in Seoul. Unless it's just hidden or only on the black market, but when I was there, I couldn't find it anywhere. Fill the front pouches of your checked suitcases with it, trust me. The other thing is, rumor has it, Korean toothpaste has no fluoride in it so you'll want to bring an extra tube or seven from home. Your teeth will thank you. Don't drink tap water, a gallon (or so) jug of water is about 80 cents, so it's all good.
PS, E-Mart is the Korean Walmart. Remember the name, they're everywhere, and visit them often. They have everything you want and need.
My last piece of advice that I can offer is just put yourself out there. Meet people, take classes, join things, try to adapt. If you go into this thinking it's just going to be a paid vacation in a city 'just like back home,' you will be sadly mistaken and in for a shocking surprise. Seoul is not like your home town, but it can feel like a home away from home if you're willing to let it :)
Enjoy yourself and take care of yourself. And be prepared, you're about to go on the adventure of a lifetime.