I don't know this particular school. I do know that it is hard for employers to get FT's in Changchun, and most of the FT's at language mills are not native speakers and/or don't have degrees. Many are terrible teachers.
That said, there are a lot of bad employers in Changchun. I've never seen anything as confusing as the salary scale you put in your OP. If your base salary is 4200, what do you have to do to get that? And what do you have to do to get the higher amount? An 800 rmb apartment will be pretty undesirable, and that is before gas, electric, water, etc bills. It is not the standard deal in CC. DSL through the phone company is available and costs about 100 per month if you do a year contract. You have to have a phone installed in your apartment to get it, though. Some apartments already have phones, others don't. Apartments are normally school provided, usually you pay the utilities. You want to be sure you have air conditioning. Winter heat is not an issue, that is automatic and free to you. I wouldn't be surprised if the school doesn't offer medical insurance, but you need to clarify that. Dental is not standard. And don't forget medical evacuation coverage. CC is the boondocks and you want to get out of here if your taxi gets smashed while passing in the oncoming traffic lane.
If you haven't read Raoul's Changchun summary already, start there. Since he was last here there are many more options for goods. There are 3 Walmarts, a Chinese chain grocery with good selection, and a City Supermarket with mostly American imported foods like soup, jello, cheese, NZ butter, pasta, etc. The weather is still cold, except when it's hot in the summer. The coal haze still lingers over the 7 month winter heating season. Clothing larger than American women's size 12 is not available. Sorry, if I had more info on your age, gender and teaching preference I could help more.
The food is ALL VERY SPICY. This is a problem for me. For many people it is not. There is no food item that I really wanted that I have not found. Finding common household items that you know are made in China can be, let's say, challenging.
I like living in CC. I don't like heat and I really don't like humidity, so it works for me. People are almost all considerate and friendly, but few people on the street speak English. The younger FT crowd spend a lot of time at the bars. The rest of us are few and far between. There are very few things to see or do in a tourist sense.
That's the nutshell version. If you are interested in teaching at the Uni, I think they are still hiring. Send me a PM and I will try to get you hooked up. Or, if you have other questions drop me a line. Sooner is better than later. I'll be hard to reach after Tuesday (US time) for about a week.