I would suggest that you begin by having an indepth meeting at each of your three corporate locations, soliciting the needs, as seen by the personnel at those locations, so that you can begin to formulate your business plan. The folks at the “front line” typically know what the problems are as well as the needs, from an IT perspective, and can provide invaluable insight. I would couple that with what management is telling you about where they want to go as a company. Lastly, I would spend some time with your hardware and network vendors to see what they feel is a prudent course of action. They will normally be able to come in and assess the usage from their perspective and let you know what you will need to do to accomplish your management’s aniticipated growth.
The combined input will tell you what needs to be addressed, what needs to be planned for (such as a predetermined 15% growth, etc.) and then you can use that to determine the capabilities of your network, system(s), personnel, etc.
The 6 to 8 weeks to put together a complete business plan is pretty aggressive since it sounds like you are new to the organization and to this level of position. I would suggest that you ask for an additional 6 to 8 weeks so that you can look at all sources of input before making and presenting your plan. The last thing you want to have happen is put together a plan that leaves out some very serious problems that you’ve not even been made aware of yet. That would leave you looking and feeling inept at best. Take your time, solicit all the input you can from management, supervisors and workers before presenting your plan. It’s better to take a little longer and present a realistic plan than it is to present a plan that is “off the wall” in a very short period of time.
Good luck with your new adventure.