C/C++ :: Including Main Header File Which Includes The Including Head

I have a main.h file where I include all the needed things to make my program compile properly, string, vector etc.

And I also have another header file which comntains a class that is used later in the code (globally), I decided to keep it in another file to make it more clear and easier.

I need to include that file in main.h, but I also include main.h from that class header file because it contains some other includes that are required to compile.

Is this a good thing? Or should I keep main.h out of that class header file and include just things required for the class?

I may have complicated it too much, so I'll show an example, what I do now:

// ---- main.h ----
#include <string>
#include <vector>
#include <ctime>
// other includes, these are just examples
#include "MyClass.h" // the separated class header file

[Code] ......

So, from what you can see MyClass.h requires just including the vector, but to avoid repeating myself I include main.h which does that already, but also includes MyClass.h

So, I have two questions:
1. Is it ok to include in that way (including a file that includes the including file)
2. Is it good to include a main header file with all the includes even if I just need one of them, or should I skip including main.h and include just the things my class requires (vector is just an example)