Size is a critical factor in determining properties of materials, both quantitatively and qualitatively. In our study of metal halide perovskite nanostructures, we found some interesting fundamental changes in properties when the size is varied from >4 nm for perovskite quantum dots (PQDs) to <2 nm for perovskite magic sized clusters (PMSCs) and even slightly smaller ligand-assisted metal halide molecular clusters (MHMCs) with much stronger quantum confinement effect (QCE), as exemplified by cesium lead bromide (CsPbBr3) and methylammonium lead bromide (CH3NH3PbBr3). Besides the expected blue shift in absorption and emission with decreasing size due to QCE, the photoluminescence quantum yield and excited state lifetime decrease generally with decreasing size, attributed to increased surface defects as well as changes in the electronic band structure with size. In addition, both the PMSCs and MHMCs are found to exhibit intrinsic chiral property based on circular dichroism (CD) spectra while the corresponding PQDs do not. Possible explanations for the origin of the chirality include asymmetry induced by liquid-liquid interface. Chiral nanoclusters are potentially useful for emerging technologies including spintronics and spin-optronics. Furthermore, we compare carrier spin dynamics of these nanostructures determined using ultrafast laser techniques and found major effects of size, phonon, nuclear spin, and surface in their lifetimes attributed to different spin relaxation mechanisms.