We use a coarse-grained model of DNA-functionalized particles (DFPs) to understand the role of DNA strand length on their self-assembly. We find that the increasing strand length for a given particle size decreases the propensity to form ordered crystalline assemblies within the simulation time. Instead, disordered structures form when the strand length exceeds a certain threshold, consistent with the previous experiments. Analysis of the simulation data based on a pair of DFPs suggests weakening interparticle interactions with increasing strand length, thereby shifting the suitable assembly conditions to lower temperatures. We find that DNA (un)hybridization kinetics at these lower temperatures becomes significantly slower, preventing systems with longer DNA strands from crystallizing successfully. We suggest that a suitable strategy to overcome this kinetic barrier is to enhance interparticle interactions for DFPs with longer DNA strands, which is achieved by increasing the DNA grafting density. We directly test this hypothesis and show successful crystallization within the simulation time for DFPs with longer strands with higher grafting densities. Our results highlight the power of computational modeling in elucidating the fundamental design principles and guiding the assembly of nanoparticles to form complex nanostructures in cases where experiments alone have not been able to do so.