It's good to see that you're approaching the project in a responsible manner.
Regarding the indices, I would further suggest pushing them further into the corner. It's more practical when holding some cards in hand, allowing you to keep them very close together instead of spread out.
You mentioned "3 layers of 280 GSM blue core paper" - I'm curious about this. It's it three layers of paper, each weighing 280 gsm, or is it a three-layered paper weighing a total of 280 gsm? If it's the former, they'd be nearly impossible to flex and shuffle they'd be so thick and heavy. If it's the latter, it's actually an inferior quality to standard Bicycle stock.
Ive been told that back when USPC was still measuring stock in grams per square meter, they were using 325 gsm for mass-produced Bicycle decks but switched to 300 gsm when they moved to the new factory in Erlanger, Kentucky due to an issue with using 325 gsm stock in the presses. The paper core they use is black rather than blue, consisting of a paper glue blended with graphite dust, rendering the cards impervious to light from all typical consumer-use sources.
