Storage usage of methods compared to copied code
It.... depends

A call to function involves a few things


Save the context
Move the parameter(s) to the appropriate registers
Enter the function
Execute
Eventually save the return value to a register
Restore the context
Eventually copy the returned value to the variable


As you can see, quite a lot of things. The bold points are the ones executed also if you don't use a function.

Please note that if these functions are "methods", you have also a "hidden" parameter (the object you are applying the method onto)

So why use functions? Well, you will have to write this code in flash only once instead of more times.

What is best? It depends on your application.


You are calling this function only once? Don't use a function
Your function is really short (for instance, a one-liner)*? Don't use a function
You are running out of flash memory? Use a function
You need a lot of speed? Don't use a function (you add overhead)
You are not in one of the previous cases? Do as you prefer


With one-liner I mean something like, for instance, byte sum(byte a, byte b) { return a + b; }; in this case the function also occupies more space, since the call function instruction is compatible with the byte sum



Please note that usually more readability is more important than performances, so maybe using functions should be encouraged. I mean, in your case I'd probably use them unless there is a problem

What to do if you don't want to use a function? Well, there are other techniques:


Mark the function as inline; this is a hint for the compiler not to create a function but to replicate this every time. This is only a hint, so the compiler may ignore this
Instead of a function write a macro. This will be substituted every time, but the code will be maintainable. As a drawback, it is much harder to debug with the usual methods.


Just a remark: usually smart compilers can guess what is the best option (inline or function) on their own also for non-inline functions. So you can also trust the compiler in 90% of the cases