I want a core switch with following specifications :
Can someone help me with which switch shall I choose, or stack in order to fulfil the above requirements.
A 3850-48XS would work for your requirements. It has 48 SFP/SFP+ ports, so it'd have some ports left over for expansion.
It has good routing features and routes at line rate.
Take a look at the 4500-X.
IMO the 3850 is not a viable option. It's an access layer switch, not a core/distribution switch. The buffers on it are too small to be a aggregation point.