There is one main route for Santa Cruz with several sidetrip options listed in the Lonely Planet Trekking in the Central Andes.
The only essential sidetrip is up to the hanging valley at the foot of Alpamayo. (Actually, there is an obvious short cut traverse from that valley so that you do not need to climb back down to continue the trek.)
Our route is the same as Lonely Planet except for night 3. Everyone was avoiding Paria campsite in 2005 due to mosquitos. Pass it by & camp at Cachinapampa.
Plan for a minimum of 3 nights in the tent. More if you want to add sidetrips. Bring food for an extra day just in case. We would camp an extra night at Alpamayo base camp or one of the other sidetrip valleys.
Note that the excellent sidetrip to Alpamayo base camp & higher up to Laguna Arhueycoacha is 2-3 hours maximum without a pack especially using the short-cut listed below. Lonely Planet wrongly lists it as 7-8 hours.
Santa Cruz Trek
Night zero sleep Huaraz (3090m) or Caraz (2270m) ... Caraz is closer to the trailhead. We stayed there
... sleeping in Huaraz is better for those still acclimatizing
... shared taxi to Cashapampa (1-2 hours from Caraz) Night 1 tent Llamacorral or stop sooner at dozens of excellent campsites along the river
... manditory sidetrip to Alpamayo Base Camp (South side)
... take the short-cut traverse from the hanging valley rather than descend to the main trail where you started Night 2 tent Taullipampa
... over the high pass early next morning for clear weather
... skip the signed Paria campsite, reputation for bad mosquitos
... continue an hour or more to the next public toilet, at an unsigned campsite but which we believe to be called Cachinapampa Night 3 tent Cachinapampa (not Paria) ... hike to Vaqueria, transport out should arrive around 11AM
... this is a fantastic drive through some of the best mountain scenery in the world!
Night 4 sleep Caraz or Huaraz
Santa Cruz Trek is not complicated. You can camp almost anywhere you wish. Decide as you go.
In Patagonia we could hike until 11PM at night. But here close to the equator it gets dark early year round.
Plan time to acclimatize to altitude before the hike. Spend some days in Huaraz (3090m) organizing your trek.
If possible, do a shorter hike sleeping as high as possible before you hike Santa Cruz. Laguna Peron or Laguna 69 would be a good choices, as they are close to Caraz.
Understand that if anyone is stricken with altitude sickness, you must head downhill on your own. Do not count on anyone being able to carry you.
1) Alpamayo Circuitcombines Santa Cruz with Alpamayo Base Camp to return back to your starting point in Cashapampa 140+km in 8-10 days. This is a great trip but long. But for most hikers it is better to do Alpamayo Base Camp and Santa Cruz as two separate hikes.
2) From Vaqueria you could hike rather than drive back down to the Llanganuco lakes we do not recommend it though it would have been fantastic before the road was built. You could add an extra night at Laguna 69.
3) You could reverse the normal route, starting in Vaqueria. We do not recommend it though many choose to do it this way as transportation is easier. The climb to Punta Union is steeper & less climactic.
Do not miss the sidetrip at least to the valley below Alpamayo Base Camp south