Similarly with variable and procedure names. Short names are not necessarily unhelpful in context. Well, two of them, anyway. Consistent use of a name is also sensible. Other styles are more concerned with personal choice.
Readability is always the defining characteristic of a good style.
Separating the code over several files makes no difference to the running of the program or the memory used. The reason is twofold. Firstly, it allows the code to be broken into a number of chunks. A small file is more easily read and edited than a large one. Global variables are more likely to be missed in a large file.