I have a question about living expenses. Generally what is the best percentage of income should rent/mortgage payments be. In other words, should rent be 20 % of income to be comfortable, or should it be more or less?

It might have been 20% at one time, but now they will lend 5 times an annual salary for a mortgage.the % must have gone up massively.

A mortgage company will lend you way more than you can afford to pay...

Dave ramsey teaches your mortgage payment be no greater than 25% of take home pay...

25 percent is the rule of thumb.