I suggest mastering the alternate piocking first, and when you're confident and your finger are nimble then have a crack @ sweeping. You need both co-ordination and speed to execute sweep. Although you can practice at very very slow speed, I can imagine you won't last long practicing like that, trust me I did that when I first started guitar. THe boredom kills you before you get somewhere.

It's all upto you now what you want to practice. And if you still wish to sweep use the search function... There has been alot of sweep question in the last few weeks.