Is it OK to use RS485 with separate wires for each device?
Both of these will work providing you apply the modifications in red: -

Both distant ends of the cable need a suitable termination resistor to protect data reflections causing corruption of the data messages.

Can I use single RS485 transceiver IC ?

The same RS-485 interface IC can be used for master and slaves alike. You can even take the cable interface onto your PCB like this: -

It makes no difference where the master is (middle or end) providing it's using an RS-485 line interface chip. The same interface chip can be used for interfacing the master or the slaves. It makes no difference because RS-485 outputs a current drive signal to the line.