You'll be at close to 9,000 feet altitude. It isn't a true canyon, in spite of its name. But it is awesome. You can cover it in a day.

Take plenty of film, so to speak. The pics won't do it justice.

Zion is great. There are many trails back into awesome waterfalls. Plan ahead and be ready for eventualities. But Zion is amongst the best of the best. Plan on staying longer there.

Never been to the North Rim. The South Rim is where all the cool trails are and the long roadway with dozens of lookouts. Unfortunately, the South rim will be choked with tourists. Unless you take an adventurist trail, that is. Google's your friend here, I think. The North rim is higher elevation, IIRC, and not as many tourists.
It's 17 fucking miles across at the widest!!

Excited about the north rim, will be there 2 nights, one at Bryce 2 at Zion.

as long as you like hiking steep climbs in the desert in the hottest months of the year... like triple digits. Might want to consider a cooler time of year like early-mid spring or late fall. It wouldn't be so bad if you were floating the river but hiking, ummm.

Average temps then at Bryce and North rim are pleasant- cool nites, zion around 90 daytime/60 at nite so no problem. We are probably going to do the Narrows hike at Zion so we want it to be warm.
Pass on the river floating, like being active!

just trying to give a heads up about the blistering heat and how last year's temps are likely to be a repeat this year. Carry lots of water!! I also recommend bandanas, several. They have endless uses including cooling necklaces. I lived in the Anza Borrego many years ago, night temps got to about 118F and it was often 12?F in the daytime, can be a major strain on the body. Late Sept is probably a good time, as you said, nights should be cooler by then. Have a great time, it's soooo beautiful there.

(retired firefighter/paramedic/girl scout here!) I am so excited- and its only January. We have a pioneer cabin at the north rim GC, are staying at BnB at Zion, and BW Grand at Bryce at this point.

We are open to ideas for LasVegas near airport the nite before out early flight (prefer no casino).

I haven't been to Vegas in over a decade, they didn't even have a pyramid then! Last time I was in that area, the airport was way far away from the "strip" don't know what it's like there now, could have been some development out that far in recent years, they did have a boom in development about ten years ago.

Good luck all the same!

was there last year mid-September. Temperatures were fine. Check out Kolob (I know, I know...) Canyon on the north side of Zion for a couple of fun hikes. VERY few people there, as opposed to the main park. Have fun!

but being good americans, I'm sure they like money enough not to care.

are concerned about them caring about.

Will we need to haul around beverages?

want to consider doing that, maybe have you own lodgings but it isn't too terribly far from Mesquite, might be more tolerant there. I know rural UT is pretty rough and tumble in spots, and also religious sensitivity is stronger than in SLC, probably the most liberal area in UT. Be careful. In UT there used to be some pretty strict alcohol laws, and watered down beer. You will be best advised to look into what hauling your own booze might require as there could be laws that prohibit transport. I make a point of not venturing that far south, Idaho is challenging enough and I live north of there! But I used to travel all over so I was aware of lots of laws some time ago... maybe check the tourism site on the state's official page.

We will keep everything discreet- they do have bars near most places we are going, so maybe we see if there are any carry-outs enroute.

a little longer than that but you have to go into MT or WY to get in the park, except one little corner that is basically undeveloped. I live within an hour of the park but in MT... which is only slightly better than Idaho, which is only slightly better than Utah! Awesome real estate, scary social climate... but lots of wildlife and that's what I like best, to heck with the red state issues, long as I can watch wolves and mountain goats and antelope and bison... and all the other cool animals.

Have fun on your trip!