This is great. I especially like that it follows the protocol's implementation for the most part. i.e. you still have utxos and script verification even if it doesn't actually support the array of script op codes.

There is a fully compatible JavaScript implementation that you could use as reference to extend yours: https://github.com/bcoin-org/bcoin

With my post, I tried to boil down the concepts as much as possible to save some mental bandwidth and make understanding the overall easier. We will see how that turns out