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Hi Lakshami
My other script (link at top of article) will do the hotspot and Ethernet features you ask but I don't think my script is suitable for you as it will only generate a hotspot when your not near your home router. You will need a static hotspot for what you request which this is not what my script is for Unless you don't configure your RPI to connect to your home router.

Second issue is this script currently only works on Jessie. I now have a working version for Stretch but that is not published yet. Hopefully it will be sometime this week (before end of Oct 2017). In Stretch network setup changed so you will probably find hotspot guides written for Jessie don't work on stretch.

To see if your usb wifi adapter can do AP mode, in terminal enter iw list
within the "Supported Interface Modes" section of the output look for AP in the list, which means it can be used for an access point.

To connect to the phones hotspot with a RPI just set the RPis wifi to the phones SSID as you would a normal router using the wifi icon next to the clock.
You won't be ablr to connect to the phones hotspot and the RPI be a hotspot at the same time.

To use a connected hard drive as a network drive you will probably need to look into setting the RPI up as a NAS (Network Attached Storage) which will allow all connected devices to access and save files.
To act as a media server you will need to look into UPnP servers such as Media Tomb to serve video and music but there are other options but this is separate to the requirements of a hotspot.

When I publish my script that works on Stretch it will show you the steps to setup an internet routed hotspot but I can't help with a media server or a NAS drive as I have not set these up on a RPi before but there should be plenty of guide on line.
Sorry I can't be more helpful than that.