Most any socket 1155 will be good for a sandy bridge i5-2400.
The thing you are hearing about is the situation where one wants to use an older motherboard with a newer ivy bridge cpu.
Yes, they are compatible, but older stock may not come with the bios update enabling ivy bridge support.
For you, I suggest using a motherboard using the latest Z77 based chipset. It has many features that you may never use, but it costs no more than many older motherboards. By now, any bios issues have been ironed out.
Cases are a personal thing. Most any case with two 120mm intake fans, or the equivalent in output fans will have plenty of airflow for your needs. It is not wrong to buy a case on looks, if that appeals to you. You will be looking at it for a long time.
From a functional point of view, there are many $50 cases that are of good quality. The Antec 300, for example.
For me, I like small cases. After all, how much do you want to put in it?
I like M-ATX as a motherboard size.
Here is a ASRock Z77 Pro4-M for example:http://www.newegg.com/Product/Product.aspx?Item=N82E16813157306
For a case, I can personally recommend the Silverstone TJ-08E.
It is very quier and easy to work with.
Here is a review. http://www.anandtech.com/show/4533/silverstone-temjin-tj08-fat-case-in-a-little-coat