Hi hzfess!
Excellent question.
1. The specific amount that you will need to pay, however, will depend on many factors, including the amount of wage earnings and withholdings from your W-2 jobs.
TurboTax has tools for this. Check out the Self Employment Tax Calculator or TaxCaster Tax Calculator. They will help you determine how much to pay and when.
2. The government operates as pay-as-you-go. As income is collected, they require their cut at least on a quarterly basis. Generally, if you expect to owe more than $1000, then yes, you should consider sending an estimated tax payment to avoid underpayment penalties.
