Oh, that's one strange datasheet; you'll get totally lost into the complexity of that chip, forgetting you are also designing a DC/DC converter! If you look at the datasheets of DC/DC controller chips, without all that CAN bus system on chip stuff, they do have clear schematics, layout examples, and what's best, sections discussing and calculating component values such as input caps, output caps, and inductors. Sometimes these application notes are very good, sometimes unusable, but you'll at least have an idea what you are doing.
I'd suggest you Google at some appnotes, for example using keywords like "buck converter input capacitor".
In a buck, the input cap is one of the most crucial components, much more critical than the output cap. Layout is equally important. This is because the switches pull hard, square-wavish current spikes from said capacitor. Theoretically, you'd aim for zero ESR and zero inductance; in real life, a combination of very low-esr, very low-Z MLCC, and a damping higher-ESR elcap is a good idea; the damping is especially important if there is any chance of this being hot-plugged.
For capacitor value, you'd want to choose maximum input voltage ripple seen at the cap (say, 0.1V for example), and solve C from I = C*dV/dt, knowing the switching period and switch current. This is a rough assumption ignoring the circuit feeding the C, but nevertheless works for the first-order design; you can always choose to double that capacitance, for example.
Using different sizes of MLCC in parallel isn't a good idea because they may resonate with the parasitic inductances present; but using a large size elcap isn't a problem because it has a lot of ESR.
With elcap in automotive environment, use known-good brands, with high temperature ratings, long operating hour ratings, and derate ripple current spec, for long life.