If you are looking at hosting, you're going to have one question to answer first and foremost ... Why host with you and not somebody else ? What value added services do you provide that the established guys don't.
Once those have been answered, and you believe you have a business case, then you're going to have to decide on what sort of service you plan on offering your clients.
What are your Service Level Agreements ?
What sort of uptime do you guarantee ?
What sort of performance do you plan on providing ?
What type of packages would you like to provide ?
How much do you plan on charging clients / How much can you charge them before they go looking elsewhere.
Once you've got a brief idea of that, you'll want to think of hardware costs.
Do you plan on reselling another provider's services ?
Do you plan on owning your own hardware ?
Will you host this hardware at home ? Or will you rent out room in a colocation facility ?
What sort of hardware will you require to be able to provide uptime/performance you want ?
What sort of bandwidth will you need to have available.
Will you need to purchase static IPs ?
Is any of this cost effective ?