Let others do the heavy work: use a software solution.
There are many out there, so start with exactly what you need to know (the information you need to have available comes first, then you determine what and how to track). Do some research on the available software and then call up a few companies and explain what you need, asking how they solve that problem.

Think of your priorities here: the right solution should be simple to manage, give quick access to information, not require a lot of interpretation, etc.

Beyond the software, think about what you can plan for to help give you the information you need. Build certain budgets to help manage how you categorize and view different invoices and areas of cashflow.

Remember, the key is to have immediate information, not just data.

Hi,
Many software solutions, "Sage" comes to mind first, have solved this problem almost 10 years ago. So if what you are trying to achieve is limited to what you've mentioned in the post, a simple accounting software will get the job done.

Someone more junior in your organization can do the actually issuing, you can see all revenue - costs - etc with a single click.

Hi - I'm work for Fortune 500 companies to analyze income and expenses to be sure the company is running optimally. First I always recommend a program, even something as simple and inexpensive as Quickbooks works. Whatever program your accountants use, you can usually pull data from to start your analysis. You dont actually need to make entries in it to be able to extract the data to analyze.
Second, you need to know where you have been to know where you are going. This means you need to look at every month for at least the last year (ideally two) - income and expenses (this can easily be pulled from a program such as Quickbooks which I assume your accounting team would use to keep the books).
Third, once you have charted income and expenses for the last year or two, you can see what has caused the largest swings up or down. Has one expense item been steadily increasing? Why? Has one line of income been decreasing? Why? Then you can start to focus on that to find savings or additional income to achieve your goal of positive cash flow.
I would build out a spreadsheet basically to dump in the numbers from the accounting program every month so you can keep a "running" spreadsheet without having to re run the reports every time.
Happy to jump on a quick call for any follow up questions!