Once the work breakdown is completed, you can construct a timeline necessary to complete the specified tasks and eventually the project. There a couple common methods to formulate this timeline, most notably the Gantt Chart and the Network Diagram.
Gantt Chart
A Gantt Chart is a bar chart that illustrates the elements of project schedule with start and finish dates. The Gantt chart should show dependencies between elements as well as the completion status of each element. But, the Gantt chart can become unwieldy on larger projects, not to mention multiple projects. It also fails to represent the relative size of work elements (only time).
Project network 
A Project Network is a graph depicting sequence and dependency of elements. The Gantt chart should show dependencies between elements as well as the completion status of each element. The project network avoids some of the ‘scheduling’ constraints of the Gantt chart, but that also becomes a weakness.
There are numerous project management software packages available. If you are looking for one (or a new one), check out this list.
Regardless of which one you chose, you should use it as a tool to manage your project, not just plan it. For instance, you can determine and monitor the Critical Path. That is, for each element, you establish the minimal and maximum time, and then identify the sequence of elements that add up to the longest overall duration. Any delay will have a direct impact on the overall schedule. Thus, you need to manage and update your project schedule throughout the lifecycle and across projects to identify potential problems.
Posted by Jack Barber 

Until you understand the big picture, there is not much sense diving into the details. For instance, my wife and I like to take vacations, but would often end up frustrated until we understood our different ‘scope’ for our project. For me, a vacation is about doing stuff. For my wife, it is about not doing stuff. Once that became clear, we were able to establish requirements that fill both our needs.

One way to derive an answer is to work backwards. Start with how many projects that you need to meet your business objectives for next year. Given that, how many proposals do you need to for that number of project wins? Now, determine the number of sales engagements required to create the opportunity for that many proposals? Eventually, you can come up with how many leads that you need.