2. When I need to pay out the rewards I can go to coins tab and right click the address from which I intend to pay out and just select spend. The money sent will be just from that one address.
Basically, yes. In the "Coins" tab, you will see the same address more than once if it received more than a one transaction. You could also select all UTXOs for a specific address at once by going into "Addresses" tab, right-clicking it and selecting "Spend" instead of selecting them manually in the "Coins" tab with CTRL and LMB.