What information exactly does an instruction cache store?

It literally stores lines of machine code from program memory (aka the entire instruction you line in your original post.

The fact you even discuss "storing all possible op codes in cache" points to a deeper misunderstanding. Talking about storing all possible op codes in cache (or any memory for that matter) has no meaning. All the possible opcodes that the processor can run are hard-wired into the logic circuitry of the processor. They aren't "stored" anywhere.

The Instruction cache stores the most recently used instructions and their addresses so that if an instruction needs to be repeated it doesn't have to be retrieved from main memory - this is much quicker.

For example the first time a loop is performed the instructions will be retrieved from main memory and simultaneously placed into the cache. On subsequent iterations of the loop the instructions can then be quickly retrieved from the fast cache memory.

The addresses are stored in the cache together with information that indicates whether the cache is up-to-date so the CPU control knows whether it can use the cached instructions or needs to go to main memory.

The instruction cache stores the individual instructions for the CPU of the currently executing program. It is the program itself. Main memory is often too slow (or has too much latency) to be able to feed the CPU its next instruction every time it is ready for one. This is why a fast cache near the CPU is used, this is the instruction cache.