is php support mail() function on this site ? thank.
Ofcourse. But only for non-spam mail)

How mutch mysql database space?
DB space like your web-space. If your DB is 10Mb your web space will be without 10Mg. cuz they are going to DB space.

Can i sacrifice my bandwidth for space.
No, you can't.

when one's account is being deleted, will he get a notification through email???
Yes. He will get notification with deletion reason.