What sort of job listings or openings
You shouldn't start freelancing if you dont have a client lined up or a network of potential clients. Job boards aren't great as they typically are low rate contracts of companies looking to get a discount. If you do good work your clients will spread your name for you.
without whatever employer benefits
Either price it in to the contract or get coverage through a spouse. (Depending on country) you need to cover your own health insurance, vacations, unemployment, additional self employment taxes, business expenses, and risks that you have gaps between contracts.
If you make $100k as an employee you may need another $30k in expenses, targeting 70% billable hours. $185/hour × 50 weeks × 40 hours × 70% = $130k. Numbers are examples only.
Some projects try to make this easy. Check out this list / tag: https://github.com/topics/good-first-issue
People who know the code can quickly determine if an issue will be easy. Some things that may seem easy will be difficult, so as an outsider it's hard to guess. Working on issues tagged good-first-issue is the safest bet that the issue won't be overly complex to solve and that the maintainers are willing to work with new contributors.