Tl:dr

How did Satoshi/the community decide an appropriate block-size-limit?

Why does the protocol increase mining difficulty by adding zeros?

I’ve some limited experience with some of the cryptographic concepts underlying bitcoins protocols.

I have two questions.

Given the fact that there is an upper limit on block size, perhaps the easiest way to breach this is to arrive at an some exceedingly large nonce which will become necessary due to other block contents. The question is, how do you set an appropriate limit for arbitrary blocks?

Would you need to know about inverting the hashing-algorithm in order to prove the efficacy of a given limit for an arbitrary ledger/header/nonce set?

Second question is about the relevance of increasing the leading zeros over time. Would it not be equivalent (wrt work done) to set a total number of zeros? That is, would you need to know about inverting the hash algorithm in order to prove that difficulty is increasing by adding leading zeros as opposed to any other “pattern” of any other hex character of the same cardinality?

Please forgive and correct my understanding of the issues in question.