A key factor that determines the radii of a micelle is the critical micelle concentration. The other is the the hydrophobicity of the micelles which can be measured using the contact angle. A lipid nanoparticle has a minimum size on the order of 50 nm due to the surface tension of the lipid bilayer. However, micelles can be much smaller.
As for the creation of uniform nanoparticles, I am going to claim that what I say next can be in no way a reasonable answer to a HW problem. Why? Because the information is hidden in some obscure PLoS paper (Stapleton and Swartz) with 7 citations using IVC. Typically, micelles created for emulsion-PCR are created by vigorous mixing and followed by an extrusion step. However, this creates a polydisperse droplets. Alternatively, if you were to use a microfluidic device, then more monodispersed droplets can be formed. The control of droplet size can be achieved by varying the flow rates of the aqueous phase and the oil phase as well as changing the surfactant.