Antenna
I have not used this type, so I cannot quantify the loss of signal quality with the connector. My guess is that it will likely not be noticeable. I am only saying it is less than optimal, because I am assuming the tab will cause minor impedance matching issues. However, this should not cause a big problem as it is only a short distance. In general, connectors will not be the source of problems at this frequency.
You cannot have the screw short the antenna to the ground plane. To solve this problem you should be able to manually route an area out of the copper to isolate the connection or you could try using a paper washer where the screw would contact the ground plane. The antenna should be connected to the ANT pin and nothing else.