In practice I've found traceability on LN to be quite a bit harder than onchain Bitcoin, as the way nodes bundle transactions up when settling channels makes it unclear who the sender and receiver of any given amount are, in a similar way to CoinJoin/mixers. I haven't tried Cashu though I hope it maintains a similarly high level of opacity. This is safe enough for a few use cases but I wouldn't put it on the same level as Monero (especially with FCMPs++).

If building on top of Monero, there would probably need to be a custom L2 solution for invoices/contracts to allow for staking as Betanet requires (I don't know of any existing solutions, do correct me if otherwise). There's somewhat of a risk here that this could negatively impact the privacy benefits Monero provides, so I would say to take a look at some of Monero's forks (Oxen, Equilibria) that have done similar things with a decent level of success.