I will preface this by saying that i never built anything related to this, nor am i visually-impaired so take whatever i say with a grain of salt. However i have been interested in the subject on & off for quite sometime following some hype around Braille tablets a decade ago.
(which sadly never materialized)

> 30 units of display thingy

They are usually called "Braille Cells" (sometimes called "piezoelectric braille cell") and have 8 dots (instead of the usual 6 for books) [https://en.wikipedia.org/wiki/Computer_Braille_Code]
These cells are comprised of 8 levers. The "Dot" rises when a voltage is applied to a crystal that expands due to the piezo effect/bimorph.

Here is a video of someone taking apart a couple of them and showing the insides, driver etc.. https://www.youtube.com/watch?v=TmwFsTLkpa8 (it's not an in-depth look but just to get an idea)

You can read about how it works in more details here : https://cdn.intechopen.com/pdfs/9307/InTech-Analysis_and_des...

Okay now what?
Well you could acquire some from ebay like this one i guess https://www.ebay.com/itm/255908240759?hash=item3b9551dd77

Or try to find something from Metec, i have seen their P20 as well as the B11 Module used with arduino projects several times, here is the website https://metec-ag.de/en/produkte-braille-module.php

They also sell "Braille Lines" which are combos : cells + backpanel/driver : https://metec-ag.de/en/produkte-braille-zeilen.php
(If you find a way to buy them i would greatly appreciate you sharing it)

PS : These cells use 200V DC to work so your project will need a DC-DC converter. You can search for similar speccs to the official one on aliexpress or whatever https://metec-ag.de/downloads/dcdc-converter-5to200v.pdf

Finally you would need a brain for all this which could be the raspi directly or you might opt for using the raspberry-pi (for the ebook manipulation, character-to-dot conversion etc.. unless you decide to pre-format the files) in conjunction with an arduino (for the signal transfer/propagation.. you know sending the dot configuration)

Take a look here for some software inspiration (it also explains the signals the braille module would be expecting but you are better off looking at the Datasheet for anything serious): https://github.com/bertrandmartel/metec-braille-driver#more-...

Good luck.

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Some more resources :

A nice video from "Applied Science" about a one Cell driver DIY project (He is i believe, using the P16 cell from metec) might help you decide whether to buy a backplane-driver or make your own [also the idea of putting a push-button underneath the braille-cell might be interesting to you for a selection mechanism maybe?] : https://www.youtube.com/watch?v=Ss-Fux86doQ

A video showing Metic P20 cells + backpanel + DC step-up converter driven by an Arduino Uno (it has no value other than to hopefully encourage you to pursue this project :D ) https://www.youtube.com/watch?v=3zqth08wQBs

Designing Braille System using P20 Braille Cells Presentation (a student project i think with a good overview of the minimum necessary parts and their functions you can skip to the 5min mark to avoid the usual academia-fluff) https://www.youtube.com/watch?v=rAYB0g6LhVM