Low pass filter for ADC signal input
Correct and the closer to 50 kHz (but above) the easier it is to make an effective anti-alias filter. But no need to go crazy about it. A 2nd order low-pass filter set at 100 kHz will provide 40 dB attenuation at 1 MHz and 80 dB attenuation at 10 MHz and, those aliased artefacts that might sneak through could easily become lower in amplitude than the resolution of your ADC.
You need to concern yourself with the parts of the spectrum that pose a threat and if there's nothing expected above 5 MHz (half the sample rate) then why bother? But if there are things happening above 5 MHz, what amplitude do they have? If they are already 40 dB down in amplitude then the filter has an easier life reducing them to an amplitude below where they might cause problems.