how can i know whether the CFM is big enough for my nios project in max10 ?

I don't remember what ICB stands for, but it essentially the interrupt and exception vectors for the NIOS processor. The configuration memory has some headers etc that account for the difference between 0x395f8 and 0x3F68F. You really don't need to worry about the static size of your program. If it builds without error it will fit. Heap and stack use depend on what you do in your code at runtime.