Using a p channel mosfet to switch a RF switch
There is no "better" option per se. It depends on your application and design choices such as maximum switching frequency, power requirements, size, cost etc. For low frequencies and small signals, both perform decently well and BJTs tend to be a little cheaper than FETs. For high current situations, a BJT would not be suitable and you might have to use FETs or even IGBTs. But since you say you are beginner and I am beginner too and I found FETs to be cheap enough, reliable enough and easy to understand and use.
A P-channel MOSFET's state depends on the potential difference between the Gate and the Source. When VGS (depends on the rest of your circuit) is less than threshold voltage VTh (Depends on the MOSFET), the switch will be ON and otherwise, it will be OFF. So, in your case the gate voltage is either 3.3V or 0V, but you have to provide the battery voltage at the minimum to see if a MOSFET is suitable for your use case. Other than VTh, you still have to check maximum current, switching frequency etc. while deciding which MOSFET to get.
It is not strictly necessary as far as I can see but it wouldn't be a bad idea in my opinion. Again, your circuit and design choices may affect this.