Sounds like you want a tablet! PDFs are pitiful on anything below 7.9 inches and are best on something in the 8.9 inches and higher category. Think Fire HDX 8.9, Nexus 9, Surface, or iPad Air 2 size. PDFs are abysmal on e-ink screens, so an LCD/LED backlit or OLED tablet is without question the way to go on that front.
Pretty much any device you purchase right now is going to have Wifi as a standard feature. Scientific calculators are easy to come by on the various app market places. Open Office and Libre Office do not (as far as I know) currently offer touch optimized mobile versions of their applications. Apple has their productivity software such as Pages, Keynote, and Numbers on their tablets while Microsoft is hell bent on putting Office on everything. Amazon now offers WPS office as a built-in set of tools for Fire OS 4 and onwards. Google Drive/Docs can be had on Play certified Android devices. Alternatives are present: Kingsoft Office is available for a few platforms, and some smaller tools. But nothing quite like what you are talking about with Libre Office or Open Office. If you want full Libre Office on a tablet type device Windows 8.1 might be the best option.
Have you maybe considered a Windows 8.1 tablet? You would be able to load all of the desktop apps that are not available as tablet apps. And a Windows tablet would probably handle PDFs the best out of anything available right now. You can run full desktop suite applications when nothing is available as a little app. A lot of screen size choices as well.
Firefox and Chrome are both available on Android through the Play store. You can get Chrome on the Apple App Store. Fire tablets don't officially support Firefox but you can side-load it. On a Windows tablet you can get the Windows Store versions or you can just go download the apps from their websites and run the desktop versions.
Like I said... e-ink is really not the screen technology you want for the things that you envision. However, that doesn't mean you shouldn't do it and there are a couple e-ink general purpose tablets around, but I can't think of the names of any of them off the top of my head. And some of them are only sort of general purpose.
SD card is extremely hit and miss. Just have to look on a device by device basis. But, I can say that my best experience with SD cards has been on Windows Phone 8.1. It handles SD cards better than anything else, in my opinion. I don't know if that transfers over to Windows 8.1 on a tablet. The Windows 8.1 tablets that I have used have all had AMPLE internal storage space.
Truth be told, for purists it is really hard to find something that ticks every single box on the wishlist. Anyway, none of this is particularly helpful.
Good luck!