What are the Factors influencing effective capacity planning?

Inventory needs, personnel training, work schedules, salaries, accounting requirements (where applicable), output projections (volume and time), ordering needs, shipping considerations (carriers, rates, ship times, etc), customer service staffing and training (again, where applicable), overall cost of production per product (utilities, staffing, building rent, equipment rental and/or maintenance, waste, returns and inventory are just some), equipment contracts, client contracts, software: personnel logging as an item flows through the production environment, time-clock software, spreadsheet software for projections/charts), web-based services (if any), and computers.

As someone who has written custom production-tracking software for one organization, as well as someone who previously was an operations manager of a mail-order production facility of another organization, I can attest to having had to consider all of these items - and more that were, in the software development instance, printing-industry specific. So consider the specific environment you're planning for.