Hello people.
I am new here.need your advice for my flight on 7th of december.My itinerary is as follows.

7th Dec BOM-DXB EK501
Transit at DXB for 2.5 hours
7th Dec DXB-JFK EK201

i have booked on an economy saver fare.due to this i can only book my seat numbers during online check-in that happens 48 hours ago.And if i want to advance book my seats it says to pay some amount.My query is will i get a seat number if i check-in online 48 hours before or its safe to advance book.considering worst case scenario of an overbooked flight.
I'm flying for the first time with emirates.Also will i get checked-in for my complete flight till JFK with seat numbers for both?