Nevada in October?

When in Las Vegas, you will be pretty close to Death Valley National Park. By the end of October, most of the summer heat will have passed, but it is before most of the winter weather has arrived.

–B.G.–

"As I am from Australia, I have no real handle on what the weather and general conditions would be like."

Least challenging conditions imaginable around Vegas at that time. Dry with very moderate temps.
If you have time for day trips during your time there, the scenic drive and main attractions plus a short hike like Icebox Canyon at Red Rock are doable in an afternoon.

Zion is such an easy drive from there that it's hard not to recommend heading over to Utah for that week after. When going there, I typically fly into Vegas in the evening, leave immediately, spend the night in St. George or Springdale, and am hiking the next morning. Cooler temps for great hiking, particularly at the higher elevations(just be advised that it could be windy and hit 20F or lower at night in mid-October at the north end of the park), and the fall colors should be in.
If you're used to rough terrain, none of the trail conditions there need concern you.

How many days do you actually have in that following week?
Bryce Canyon is worth checking out for a day, especially for a first trip.
Valley of Fire(which is like being on another planet) is about 40 miles outside Vegas, and another great place to visit. I've gone there a couple of times in the afternoon on the way back to Vegas before flying out the next day.

Late October weather can be anything from very cold to nice and warm days.
Be flexible.
For instance, if the weather is cold, go to Death Valley.
If the weather is warm, explore the canyons of southern Utah (higher elevations than DV).
Nice thing about Vegas is you can go either way.
And, of course, there is the Grand Canyon too. Even if it's cold it would be warm down inside.

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