Hi Mike I haven't been to Big Bend, a first timers guide would be wonderful! Feel free to PM me, thanks.
PM'd yesterday. I was able to attach the PDF. It's basically a PDF that I have sent to coworkers. There's a lot to see in the park and the PDF highlights the more interesting places to see (like the waterfall at Cattail Falls). Sadly, the Castolan store burned down this year. It was a traditional stop for ice cream when coming back for Santa Elena Canyon (gorgeous and very accessible). The I've been going there for a very long time and I haven't seen anywhere near all of it. On my first overnight backpack to the South Rim I didn't take a tent (I like sleeping out when I can) and I woke up with frost on my sleeping bag. That was in September.
Hot is relative in BiBe. it's a dry heat so you lose a lot of water and don't really feel dehydrated until it's a problem. Personally speaking I carry a cooler, with ice, full of water. I also DO NOT drain my cooler until I'm on my way home (typically I water the plants at a little roadside park area that is a little south of the USBP checkpoint with it). When I hike I have a Camelbak full of water and two liters, one in each side pocket. There are some places that are simply off limits in July / August, like the Marufo-Vega trail on the east side of the park. The Big Bend Chat forum lost our moderator and friend last month because he tried to hike out to Randall's Overlook at the wrong time of the year. He almost made it back
The River Road is a nice trip. I've done that a dozen or more times. I did most of the trips with just a spare, no compressor, no tire kit. Then one afternoon in August, when the temp gauge said 112, almost to Mariscal Mine, a friend of mine said "what's that sound". I told him I didn't hear anything. He said "it sounds like air"

about that time I got a low, right front tire, air pressure warning. I was driving an '08' 2500HD Silverado back then and I had just put brand new KO2's on it. I didn't air down like I should have. A rock went into the thickest part of the outside lug in the tire and cut all the way through. If I would have had a compressor and a repair kit I could have stuffed a bunch of plugs in it and aired it up. Instead I had to change the tire in 112 degree heat and abort the planned trip to Mariscal Mine for night photography. I have on board air, tire repair kit, and high lift jack now. That said, I've seen a lot of rental cars out there.
The desert isn't a place to be feared. It simply needs to be respected.
There are no technical trails in BiBe. Some will argue that point. I live in the Four Corners (for now). I have the mountains to the north, Utah (where they invented technical trails), and the canyons around Farmington. BiBe has one trail, Black Gap Road, that simply isn't that impressive. It's pretty, just not difficult. The last time I went through Black Gap a guy in a brand new Toyota long bed pickup went through with me.
If you stay in the Basin, make sure you go outside at night and check out the stars. The central bulge of the Milky Way (Andromeda Galaxy) is up early enough in September that you aren't out at 3am to see it. More like 10pm. If you don't stay in the Basin at least drive up, check out the restaurant, visitor center, hotel rooms, and cabins up the hill behind the hotel rooms. I haven't been able to get it to work out but I have a goal of being in the Basin when it snows and shuts the road leaving down.
Try to make a trip into old Terlingua and check out the ghost town.
Photos below (maybe one timelapse)
South Rim. The loop is about 14 miles. I've done the loop 3 or 4 times. and up the Pinnacles / down the Pinnacles, a little shorter, more than that. Either work. I'm fond of up/down the Pinnacles. It's a long day hike.
Sotol Vista sunset. Sunsets are a thing at Sotol Vista. Great place to take in the view, sit in the lawn chair, and relax. They are never the same.
The Mule Ears. A friend and I hiked out to the spring last May starting at around 10am (a little too late really). It was amazing to me how many people we met on the trail with no water... crazy
East side of the park, Boquillas Canyon but no bandits will come get you. You're literally a short walk across the river (don't do that) and I've never felt threatened.
The Hot Springs
The West side of the park. Santa Elena Canyon by moonlight
Cattail Falls (caveat, this was an extra special time. The falls had good flow. Normally it's just a trickle BUT it's always a cool oasis no matter what time you go in the summer.
Old Terlingua Cemetary
Almost forgot the timelapse