Yours is a pretty different situation from most posters on this forum, but I think it is actually better to only pay the default amount on your student loans.
For a zero-interest car loan I would still advocate selling the new car and buying something within your budget. But given that you already incurred this debt, and it's not backed by any asset you can't afford, and is accruing interest slower than inflation, I see no good reason (other than peace of mind) to pay it off any sooner than you have to.