The right amount of leverage is “I won’t even miss this money”. Like 5% of your income per week in repayments.

You can probably find 5% of bullshit in your spending to cover the repayment every week without blinking.

10%, maybe that’s getting tougher, some small lifestyle adjustment needed to keep the budget working.

20%, now you’re going to start having liquidity problems in a few weeks time you didn’t anticipate.

50%, sweet Jesus who wrote you this loan? Can I short them?