Our advice has always been to purchase the latest and largest iPad Pro model, even if it means having to sacrifice on storage space or cellular connectivity because of the cost, as the latest model will give you the most hardware longevity and screen real estate. We would definitely recommend getting an iPad with the latest Apple Silicon processors.
Currently, the best iPad to use with our apps is the latest generation iPad Pro 12.9". The large screen size and fast processor has definite advantages when working with a lot of documents and videos. For storage space, 256GB is ample for most situations, but if you plan on storing a lot of videos on your iPad you may want to get 512GB or more.
The latest generation iPad Pro 11" is also a good solution but with a smaller screen size, and the latest generation iPad Air is also capable but does not have as much storage space options.
You can compare the different models here: https://www.apple.com/ipad/compare/
If you choose an iPad that is compatible with the Magic Keyboard (https://www.apple.com/ipad-keyboards/) it is a fabulous accessory with a built in trackpad. An Apple Pencil (https://www.apple.com/apple-pencil/) is not required as you don’t draw in our apps, but it does offer a preciseness when doing any kind of annotations, such as highlights and callouts.