1. XQD cards are a "pre-standard" implementation of what became CFE Type B. Sort of a prototype, developed mostly by Sony and Nikon. The surviving market for them is in some non-Nikon cameras and some medical and scientific instrumentation. They will probably always be more expensive, even though less capable. Since you are not using video, the XQD cards would work fine, if you happen to find a great deal on them somewhere. Otherwise, I'd target CFE-B.
2. This was answered above. The two types off cards are physically different.
3. I do not compress my raw files (D850...haven't bought my Z8 yet), but find that 10 files/GB is a good way to make a safe, quick estimate.
4. Similarity of this camera to other Nikon cameras varies. I'm working to get one because it is fairly similar to my D850 and D500. It is less similar to the D750. If you really refuse to download and scan your way through the manual, I suggest sitting down and scrolling (actively) through the menus. Use the "?" button to learn about stuff. Paul and I disagree on a number of things, but he is absolutely correct about this one.

I just purchased a new Nikon Z8 from the Nikon Store. The little book that came with it is useless, so I have some questions. I won't be using it for videos.

1. The camera takes CFexpress and XQD cards. What's the difference?

2. When I went on line to price cards, I saw there were CFexpress-A and CFexpress-B cards. What's the difference? Will both work in the camera?

3. About how many still RAW images will fit on a 128gig card?

4. Can you recommend a good 3rd party instruction manual? Amazon offers several.

Thanks for your help.

Please listen to and follow the advice you have received so far. I will repeat it to empathize its importance:

Download all of the free Nikon Z8 guides fron NionUSA. The Reference Guide is very important. Some of the other guides are more specialized and may help you.

https://downloadcenter.nikonimglib.com/en/products/616/Z_8.html

Buy a third party guide. I have two for my Z9. Thom Hogan's and Steve Perry's. Thom Hogan's has an extensive info on how to use flash . That may be important to you.

Unless you are completely unfamiliar with cameras, particularly in the Nikon environment, I would suggest that the operation of the Z8 isn’t really all that different from the Nikon Dslr’s. I found it pretty easy to step up from my Nikon dslr’s to my Z8, except (a BIG except) for the incredible (and incredibly different) auto focus capabilities. To begin to understand what the Z8 can do AF wise, I found Steve Perry’s ebook devoted solely to the AF function work every penny.

https://bcgwebstore.com/product/secrets-to-the-nikon-autofocus-system-mirrorless-edition/

Can’t recommend it enough. If you are not familiar with general use of Nikon bodies, you may need a more general primer, but you may still want that AF book to understand the intricacies of the 8’s amazing capabilities. I am intimately aware of basic Nikon camera design, but found figuring out how to max out the numerous AF variations to be impossible without the help.

BTW - ignore the suggestion about the free Nikon guide. It’s as useless as tits on a bull.

1- cf express uses one extra lane for data throughput and is faster. If you already have xqd they will work, but if buying go cfb, better and cheaper.

2- they are totally different beasts. "A" will not work. Period. Buy the "B" s.

3- file sizes should be roughly the same as for my d850. About 1200 per 128G card using raw compression at 14 bit.

4 - the nikon version is online only. I am a big fan of Thom Hogan's guides. Extremely thorough. Go to bythom.com.