iPads/iPad Pros are more simplified computers.
And iPads and iOS is a whole different experience to work in than OS X/macOS.
iOS is an app-centric OS with very limited multitasking
There is no native external mouse or trackpad support in iOS, either.
Your only input devices are Bluetooth keyboards, your finger/s or an Apple Pencil ( or other third party Bluetooth stylus )
TurboTax is available for iOS. Have noooo clue how good it is, or not, on iOS.
You will need a separate comprehensive PDF app that will let you print to an Airprint compatible printer for creating and printing PDFs
If you work with spreadsheets, currently Apple’s Numbers app has issues with tapping and navigating cells using the Apple Pencil. Do not know if this bug, oversight has been fixed in the current iOS 11 version of not.
You will need to purchase special wireless mobile drives compatible with iDevices and iOS.
There are a few special storage devices for mobile devices. There are portable, bulit-in WiFi hotspot hard drives for mobile devices made by Western Digital and Seagate.
http://www.wdc.com/en/products/products.aspx?id=1330
http://www.wdc.com/en/products/products.aspx?id=1660
https://www.seagate.com/consumer/backup/wireless-plus/#features
There are special mobile lightning connected and built in WiFi Hot spot, USB flash drives made by SanDisk (now owned by Western Digital)
https://www.sandisk.com/home/mobile-device-storage/ixpand
https://www.sandisk.com/home/mobile-device-storage/ixpand-mini
https://www.sandisk.com/home/mobile-device-storage/connect-wireless-stick
http://www.adamelements.com/iKlips/iklips.html
This listing maybe incomplete and somewhat outdated, now. So do an online search for similar external data storage devices for iPads
Kingston Electronics makes some data storage devices for iPads/iDevices, now, too!
https://www.kingstongo.com/us/usb/datatraveler-bolt-duo-flash-drive-for-iphone
Good Luck!