First make out what you want to do. Realistic?, Anime?, Erotic?, Sci-fi?, and select your downloads on that.
Buy one month of DAZ-Pro and you get a load of stuff. Don't forget to cash your premium and unsubscribe before the end of the month.

As for DAZ V3/M3 models, check out the reduced resolution versions in the starter pack. In most renders you will not be able to tell the difference, and they render much faster. 

For DAZ|Studio add-ons the d-Former and the morph loader plug-in are a must-have.