This paper describes a comprehensive network model which sufficiently captures the noise impairments in the physical layer due to in-line EDFA amplifiers, non-linear impairments in optical links and noise at the network nodes due to lossy ROADMs for dispersion uncompensated transmission systems. The model builds upon the LOGON strategy, helps in modularizing the contribution of noise by the ROADMs and optical links and thereby making it suitable to use for network management and planning purposes. Further, the model was used to analyze critical configuration zones where improved OSNR conditions at the ROADMs result in increasing network capacity by 4.5 to 5 Tbps. Lastly, using this model an offline strategy is suggested for adding in-line EDFAs that has a potential to help service providers demonstrating capacity benefits of procuring addition equipment upfront. The results show that at the OSNR limit this strategy can improve the day one network capacity by 36% for the BT UK network when 10% blocking is reached.