What is the upper limit of users attached to a mint?

Am I correct to assume that Ecash could be used or rather incorporated into some CoinJoin, same as Lightning and thus further drastically improve the privacy? Or am I missing something?

Indeed

I recently realized that game theory favors ecash because the mints can't become central banks because they are basically over bitcoin and lightning rails. If there isn't a "central mint", this means mints are already incentivized to be completely trustworthy. If they aren't and expand their credit ...

So my question is: what should I do to help and collaborate with cashu and fedimints?