Flash and Storage question

256kB RAM 1024kB on-chip flash, 8MB external flash

could anybody explain:

1. what is "on-chip flash" for? Is it for firmware only?
   
2. there are modules Flash, Storage, StorageFile, fs.
   all can read/write... to which flash?
   
3. does block address space include both on-chip flash and external flash, kind of concatenates 1MB and 8MB, or they are separate?
   
4. I need to write text or binary files, they may be long size. Should I use StorageFile.write()?
   
5. what type of filesystem is it? FAT, VFAT?
   
6. I could not find how to get metadata of a file - size, create time, change time. I hope at least size should be somewhere.
   
7. can I create folders?