The best lines from Lima are Linea, Cruz del Sur and CIVA, with reclining seats and clean services. A cheaper option is Tres Estrellas. More options about routes and schedules can be found at PeruSchedules.
It is not necessary to leave the 'Terminal Terrestre' to change buses. You need a taxi if you have to go into the City (US$2).
Chimbote has a modern bus 'Terminal Terrestre' 5km south of the city. There are frequent buses north & south along the Panamerican Highway. Day buses go to Huaraz via the spectacular Cañon_del_ Pato & Caraz at 8am with Turismo Huaraz, or via Casma & Callán Pass, & mainly night buses go via the paved road to Pativilca. You can catch a 6am Transportes Linea bus from Trujillo to catch the 8am bus from Chimbote up the spectacular Cañon del Pato to Huaraz in the day with TurismoHuaraz.