For the tokens I just use paper but a little bit thicker as normal (200g/m² - my printer doesn't support more). I glue 2-3 layers of this over each other.
For the boards I'm using A4 printable self-adhesive labels something like this. I place them on A4 greyboard and cut the board with a cutter. For the greyboard you may use a little thinner one then I've linked 1-1.5mm should be better.
It's not perfect but it's much better then just normal paper.
Depends on what color you want. These might be the ones you are looking for, if you are in the USA: https://www.amazon.com/Chessex-Special-Dice-White-Opaque/dp/B001S70A86/ref=mp_s_a_1_11?keywords=blank+d20&qid=1653498848&sr=8-11
On another note: This sounds really awesome! When will you be posting pictures?
There was another thread that suggested getting one of these: https://www.amazon.com/dp/B07KWL7D8L/ref=cm_sw_r_apan_i_EDZM25GAEZ372Z44AS9N?_encoding=UTF8&psc=1
I got it and I'm pretty happy with it, it's a bit bigger than just the base box but I have a pouch for each faction, pouch for landmarks, pouch for hirelings, and a pouch for setup. Fits all the faction boards and actual boards fine, but they can technically slide around a little in the case.
Cardstock I used is Accent Opaque Thick Cardstock Paper, White Paper, 80lb Cover, 216 gsm. The boxes are sturdy enough that even the fullest ones (Duchy, Marquise, Vagabond) don't feel like they're going to tear if I lift them up by one side. The most likely damage I could see happening is someone just opening a box too eagerly and tearing the lid or dust flap. You have to be pretty precise with your folds/cuts or the lid catches a little bit on the dust flaps - you could cut the dust flaps out but then the box wouldn't really close, and tokens might fall out.
I bought these instead of official sleeves. They work well and I have a ton extra for future content
These work SUPER well, and getting two of them will cover all expansions! Highly, Highly recommend these (the boxes the sleeves come in fit the shared decks after you sleeve them too!)