You need to say, at least, also the min and the max value of your signal. Before to analyze it, if fact, you have to "translate" your signal voltage range into that of the ADC. Once the signal is properly digitized you can analyze it using the method that better fit your application.
The external circuitry can also provide filtering, in order to clean the signal from unwanted spurious (if needed).
Also the information about the waveform you want to analyze is useful. You are speaking about a 200-500 kHz signal frequency: if it is a waveform other than a sinewave you have to consider a certain number of harmonics that have to pass in order not to have lack of precision due to attenuation.
What is required exactly is you giving answers on those questions instead of quoting them.
The fastest and easiest way is buying a scope.
Google on TRMS and arduino If you do not want to program yourself.