The lanthanides fill the 4-f levels (and some make good neutron absorbers), while the actinides fill the 5-f levels.
Isotopes such as U-233, U-235, Pu-239 and Pu-241 are readily fissionable by thermal (low energy) neutrons. Isotopes like Th-232, U-238 can fission by fast (high energy) neutrons.
The electron configuration depends on the Z of the atom and the physics of the electron interaction with the coulomb field. Nuclear properties are independent of the electron configuration, but do depend on the nuclear structure which is related to the number of protons (Z) and neutrons in the nucleus.