I think a fully custodial wallet is what I want.  Where I can transfer a small amount of BTC (which is self-custody) for zapping and receiving zaps.  How does the wallet provider make money?  Do they take a percentage? 

 They take small fees from the transactions and some sell other services like swapping between on-chain and LN. We are so early, many operators are first building the solutions and care about earnings later.