1.It can be located on either side.Usually it is near to MSC to reduce A-interface E1 cost.
2.1 A-ter E1=30 circuits.
1 TRX=8 circuits
Now i think you can calculate yourself.
Also take A-ter utilisation as 70%(max) while dimnsioning.
2.1 Ater E1=4 A-inteface E1.
This calculation is valid for TDM mode only.If you are using Abis over IP or HDLC,the calculated A-ter E1 will be quite less
if you are in Ericsson,let me know,as this calculation is bit different there.