The fastest possible setup yielded this.

A giant 500W Dell power supply made barely enough pixies to feed 3 raspberry pi's.  

It was a bit weird to turn pages with the buttons.  It was hard to turn pages with the left paw, but anything was better than the ipad.  A 3rd button on the left side might aid the left paw.  Ventilation was worse.  It's going to be brutal in hot weather.

It needs to be 5mm farther back.  The magnet holders need to be without walls so they can sit farther back.  There's a case for bolting it on the back so it can go a few inches farther back.  Maybe the viewing angle can be more horizontal.  Making it completely fold when not in use would require a major overhaul of the cables.

The back needs panels to keep it from sliding forward.  The corners need latches.  The confusers all need to go under the instrument instead of on top of it.  Maybe that would free up enough space for a pointing device.

As cramped as it is, it's a function of what $30,000 in annual rent can afford.  Want more space?  Pay $50,000 in rent or $80,000 after everyone moves back.

The pointing device is the next big deal.  Selecting files without a GUI is really slow.

There's not enough room for a mouse pad anywhere.  Alternative pointing devices have gotten nosebleed expensive.  The cheapest solution is the mighty $20 Perixx trackpad.

https://www.amazon.com/Perixx-PERIPAD-501-Professional-Wired-Touchpad/dp/B001CX85I8

It's 76x64mm.

Good trackpads are hundreds of doll hairs.  Good trackballs start 3x more expensive than mice & a are bit bulkier than trackpads.

It's been 25 years, but balls have retro appeal & lions remember having a better experience with them than pads.  Based on the memory, a trackball would be a better match than a trackpad for a stationary application.   All modern trackballs are just upside down mice with optical sensors pointing up.

The best trackball is the $33 Kensington Orbit

https://www.amazon.com/gp/product/B07YVMXLQC

No dimensions are given, but it's as wide as a paw.  

There is a thumb operated trackball 

https://www.amazon.com/Wireless-Handheld-Finger-Trackball-Pointer/dp/B0057KL2AU/

But this would be impossible to draw annotations with.

There is a lot of interest in reusing macbook track pads as standalone devices, but the track pads themselves are SPI devices connected by a very fine pitch ribbon cable to the mane board.  The brain that converts the keyboard & trackpad to a USB signal is on the mane board.  

The touch pads extracted with the LCD panels have undocumented ELAN 33059 chips but appear to use I2C.  The internet has never figured out how to use these.

There was a desire long ago to make a pointing device out of a webcam that tracked a blinking LED.  It might be too low in resolution & too consuming of space.

Both trackballs & trackpads are harder to draw on than mice.  Given the need to draw annotations, using a phone as a trackpad may be the best option.  An interface which takes both a stylus & paw is a big win.  The phone can also show the recording interface.  There's a lot of adware for using phones as trackpads.