What would you say was the hardest part of building the computer? How many breadboards did you end up using?
You should put a couple of inverters after the 555 timer to make signal fronts sharper. I recommend 74als series (older, bjt, easier to work with), or 74hct (more modern, mosfet-based, ttl-compatible). We even tried some 74act parts, but these are not designed for breadboards ;)
Though Ben Eater’s work is overall great and very instructive. You should follow his recommendations on breadboarding (board models, wires and stuff), they are stellar.
The hardest part, as usual in electronics, is contact quality, be careful diligent. For Nibbler we used around 5-6 breadboards.
P.S.: it was hard to source ALU. I scoured ebay for weeks and got some for exorbitant price + shipping. Then I found one factory in Belarus that still makes 74als181 (кр1533ип3 in cyrillic) chips in narrow dip packaging. I ordered a small box of these ;) It was cheaper than a single 74hc chip from eBay.