Regarding your concerns about the fee, you will only be charged according to the amount you and your freelancer have set an hourly contract, and on milestone payments. You will also be charged if you set a weekly payment on an hourly contract, or issue bonuses to your freelancer.
Upwork charges a 2.75% processing fee on all payments made. The fee is assessed any time we charge your billing method and will show up as a separate item on your transaction history and payment receipt. The fee is calculated as a percentage on top of the payment you are making. For example, if you make a payment of $1,000, Upwork will charge an additional $27.50 fee for processing the payment.
For hourly projects, billing occurs weekly, so the processing fee is assessed when we charge your billing method each week and on any additional bonuses. For fixed-price projects, the processing fee is charged each time you fund a milestone or give a bonus.