Engineering materials especially at the nanoscale plays an important role in the development of quantum technologies. To that effect, in-plane selective area growth (SAG) of III-V nanowires (NWs) is a scalable and versatile materials platform that holds great promise for nanoelectronics and photonics applications. However, achieving the requisite material characteristics demands a meticulous optimization of the crystal quality. This critical aspect cannot be overlooked, given the significant impact it has on device performance and functionality. As such, crystal quality optimization through in-plane SAG has become a topic of keen research interest in the scientific community, as it holds the potential to unlock novel and exciting applications. The first part of the thesis gives a brief introduction to the concepts of crystal growth associated with the work in this thesis along with experimental methods implemented. This includes a description of the crystal symmetry, adatom kinetics to be considered during SAG and resulting crystal shapes. The methods of SAG substrate fabrication, atomic force microscopy (AFM), molecular beam epitaxy (MBE) and electron microscopy are briefly explained. The second part of this thesis presents the study of MBE grown GaAs NW arrays on GaAs substrates. For GaAs homo-epitaxy, the effect of in-plane alignment is studied. The misalignment of SAG NWs as a result of the tolerances associated with substrate fabrication on the NW morphology is studied via AFM. The facet roughness of the NWs is used as a measure of the structural quality. The use of Sb as a surfactant during GaAs growth is found to have no effect on the nominally aligned NWs, however, it is found that reducing the NW length allows for accommodating a small degree of misalignment. Further, the possibility of engineering the cross-sectional shapes of GaAs NWs by choice of substrate in-plane and out-of-plane orientations is presented. To that effect, novel high-index substrates such as (2 1 1) and (3 1 1) have been used to grow the NWs. It is found that the polarity of the substrate, use of Sb as a surfactant and varying SAG mask dimensions can also modify the NW shape in some cases. This opens up the possibility to obtain NWs with desired combinations of facets and corresponding shapes. The third part of the thesis presents hetero-epitaxy of InAs/GaAs NWs grown on (3 1 1)A substrates. The structural reproducibility of these NWs across very large arrays has been quantified by performing AFM on 180 NWs. Varying the growth time and the SAG mask dimensions results in a variety of NW morphologies. The effect of intentional in-plane misalignment on the NW morphology is also studied and found to change with varying NW width. The NW morphologies obtained via AFM are also supplemented with electron microscopy methods to analyze the crystal quality and the In and Ga composition for select dimensions. Finally, the observed structural reproducibility is substantiated by electrical transport measurements on NW based field effect transport (NWFET) devices fabricated in a large scale multiplexer/de-multiplexer set-up operating at cryogenic temperatures. The set-up allows for addressing 128 individual nominally identical NWs on a single chip and requires 8192 NWFET devices to function. Additionally, using this set-up, measurements are also conducted on NWs with varying SAG mask dimensions and in-plane orientations and the resulting transport characteristics are found to be directly correlated with the structural and crystal quality of the NWs. The final part consists of final remarks regarding the entirety of the thesis and presents some ideas for future exploration.