Since no one has answered I will try. I am no expert so someone may correct me.
It is rarely a bad idea to have a ground fill. It will carry away stray noise.
To create the ground fill you just need to right click on a connector or pad that is part of your V- (GND) net and select set as ground fill seed. If you have more than one circuit with separate V- (GND) nets then you will need to set at least one seed for each net. After that make sure both layers are set as clickable (or which ever layer you want the ground fill on if you only want it on one) then go to the Routing menu > Ground Fill > Ground Fill (Top and Bottom).
Once it is done creating the ground fill you will see some of the ground fill is yellow and some is red. This is supposed to show if the ground fill is connected to ground or not. Unfortunately it can show connected ones as unconnected so don't be too concerned. To fix ones you know are not connected you may be able to drag via's on to the board and connect those areas on one side to a connected plane on the other side.
You can also add via's around parts that need additional cooling but again be careful they are only on ground planes on both sides and do not intersect any traces other than ground traces.
If you place these via's before creating the ground fill Fritzing can leave a space around them.