Nanocrystalline ceramics have great potential for applications in electronics, sensors and energy-related areas due to their remarkable functional properties. Conventionally, when a material designed for a targeted application, the compositions at the apex of the phase diagram is altered. Hence, the centre of the phase diagram remains as an unexplored field in this method of design. To explore the properties at equimolar regime, multicomponent alloys were developed with five or more elements substituted in a single Wycoff position. Similarly, in the class of ceramics also, only doped, co-doped and binary ceramics have been extensively studied, while the realm of equimolar or near-equimolar, multicomponent ceramics has been largely an unexplored field. In the present work, a transition metal based high entropy oxide (TM-HEO), (Co,Cu,Mg,Ni,Zn)O was synthesised using three bottom up approaches, namely, flame spray pyrolysis (FSP), nebulised spray pyrolysis (NSP) and reverse co-precipitation (RCP) with varying levels of residence times with the primary intention of studying and analysing the phase formation, structure and optical band gap properties. Phase-pure (Co,Cu,Mg,Ni,Zn)O and lower combination compositions were obtained in all the three process as confirmed from X-ray diffraction analysis. Structure analysis showed the presence of distortion in the rocksalt crystal structure which could be attributed to the additive effects of exchange striction (from the magnetic constituents) and magnetic anisotropy (from the decreased crystallite size), in addition to the Jahn-Teller effect. Optical bandgap studies revealed that copper played a major role in influencing the bandgap and that it depended on the off-stoichiometry in the product arising from the synthesis process. To understand the effect of aliovalent cations in the TM-HEO phase formation, Na+1, Fe+3 and Ti+4 cations were added/substituted in the cation sublattice. Presence of multivalency/non-stoichiometry to accommodate a different-sized cation and maintaining electroneutrality were identified as the critical criteria for single-phase formation in these multicomponent systems. Addition of Ti TM-HEO resulted in a spinel phase formation and the factors affecting the spinel phase stabilisation and band gap variation with composition were studied further in detail.