Plan capacity and responsibilities
List the people contributing to product, design, mobile, backend and quality assurance. Identify whether their time is dedicated or shared. Include coordination and review effort. A monthly retainer should explain the capacity available and the process for deciding priorities, rather than promising an unlimited list of features.
Review progress at each sprint
Demonstrations make it easier to connect expenditure to working software. Update the remaining estimate when requirements change or an integration reveals additional work. Keep a visible backlog and acceptance criteria. Review budget consumption early enough to reduce scope or change the plan without sacrificing the quality of the launch journey.
Separate delivery and operation
Infrastructure and support costs may begin during development and continue afterwards. Distinguish them from implementation capacity. When the product moves into operation, adjust the engagement to maintenance and improvement needs. A shorter feature list with a complete, stable release is often more useful than maintaining a high monthly spend without a clear launch outcome.