do i get back from the terracotta to xian, the same place where i alight, if i take the bus and what are the timings (first bus, last bus)?

Yes, it will be the same place for your boarding and alighting for the bus.
Bus Toursim line 5 (no. 306) is in operation from 07:00 to 19:00, leaving from XA Railway Station.

To take a taxi from XA to Terracotta, it costs around CNY100. If you rent a taxi or same-accommodation private car for one day, the fare shall be around CNY300 (just for your reference.)

By contrast, it is most convenient, money-saving and trustworthy to take the public bus for the trip.

Thanks so much Mike. I'll like to try to take the bus of course but I've heard of touts so am a bit concerned. There's 5 of us so we'll have to take 2 cabs too, if as a last resort.