I would like to request a feature where in when someone dials the main number, the system will ring our phones first for a few times and then if no one answers, we can send it to the company greeting and after the greeting the phones will be ringing again
I agree with your first two steps being pretty typical, but Stephen makes a good point that it is likely no one would be available just a few seconds after they were not available the first time. This also would create a loop and callers would just repeat through the process endlessly until someone answers or they hang up. This is sometimes referred to as "voicemail jail" :)
I would consider using a call group to hold calls in queue with announcements and music or letting calls go to a mailbox after some period of time.