The energetics and structure of small HeNI2 dusters are analyzed as the size of the system changes, with N up to 38. The full interaction between the 12 molecule and the He atoms is based on analytical ab initio He-I-2 potentials plus the He-He interaction, obtained from first-principle calculations. The most stable structures, as a function of the number of solvent He atoms, are obtained by employing an evolutionary algorithm and compared with CCSD(T) and MP2 ab initio computations. Further, the classical description is completed by explicitly including thermal corrections and quantum features, such as zero-point-energy values and spatialdelocalization. From quantum PIMC calculations, the binding energies and radial/ angular probability density distributions of the thermal equilibrium state for selected-size clusters are computed at a low temperature. The sequential formation of regular shell structures is analyzed and discussed for both classical and quantum treatments.