I left Buenos Aires from Retiro at about 22:30, and arrived in Cordoba at 7:00. I paid 80+ pesos for coche/cama on Chevalier, and it was very comfortable. From the bus station, I shared a 4 peso cab to San Martin 338 entre Lima y Catamarca where Baluch Backpackers Hostel is located. I made a reservation before leaving BsAs.

can you make a reservation on the website or does it have to be done by phone/person?

You can reserve through their website or their phone...

Tel: +54-351-4223977
http://www.baluchbackpackers.com