The increasing levels of congestion and infrastructure costs in cities have created a need for more intelligent transport systems. Urban Air Mobility (UAM) offers a solution by introducing intra-urban aerial transport to overcome the existing congested infrastructure. The performance of UAM systems are highly dependent on vertiport locations, vehicle sizing and infrastructure specifications. This study takes a holistic approach to UAM network optimisation by considering the inter-relatedness of these decisions. A vertiport placement model with vehicle sizing constraints is developed to determine the optimal vertiport configuration while considering eVTOL performance. The resulting configuration is used to model waiting times depending on infrastructure specifications. These waiting times are incorporated in the vertiport placement and vehicle sizing models. An iterative approach is undertaken to find the network configuration that balances the infrastructure, operational costs as well as passenger waiting times. The purpose of the study is to inform policy-making by proposing a holistic approach to UAM network design.