No. You cannot use whatsapp in Samsung Metro XL.
Yes, this phone supports the Nepali language.
Yes, Samsung Metro XL does have music player.
No. You cannot use Jio sim card in this phone.
You can store up to 1000 contacts in Metro XL. In addition, you can store up to 250 contacts in each of your sim card. So, if you are using 2 sim cards, in total you can store up to 1500 contacts.