EMC 30-50 MHz emssions
If my PCB is not too large (15cm x 5cm) 30-50 MHz emissions are mainly
radiated through power cables?

Yes, that is a general truth and, that means you need to prevent conducted emissions because on a long(ish) cable, conducted emissions become radiated emissions. The good news about conducted emissions is that you can actually simulate the results (with a little care) so, set up your circuit in a simulator and mimic the circuit of a LISN and see what the differential conducted emission levels look like (basically the current flow in one power wire).
You'd probably be more interested in CM conducted emissions because they are more likely to becomes radiated emissions however.... CM conducted emissions will very much be influenced by high-speed differential currents produced by your board/circuit and that is prime work for a simulator (the current flow in one power wire).
Guessing about what inductor or ferrite to fit here or there is really just guessing. Set up a simulation and then introduce capacitors, inductors and ferrites to reduce differential conducted emissions.