Not sure how far you've read, but it is not at all certain that Voldemort wants to challenge Harry. Whatever his plans are for Harry, they don't involve killing him -- at least not in the near term.
I meant challenge as in, be up to the job of opposing him. This Voldemort does oppose Harry's plans, long term, largely because he doesn't get the idea of making the world better for everyone, he just wants out.
The methods Harry would employ would achieve Voldemort's aims as well, and if Voldemort's horcruxes work as advertised, he shouldn't care too much about the time frame.
Sure, and Harry would see that. Voldemort would not. He wants a subverted Harry on his side, but he doesn't care about rebuilding the universe to be nice.
