I have started a successful small business (a summer camp online) this past summer. I didn't make a business plan and I didn't incorporate. I just found staff, built a website and marketed. It worked and worked well....everyone happy.
If you are still exploring the viability of this business, then Id suggest that you wait till the business generates its first cheque - or you will be hiring and need to do payroll. On the other hand, if you have the clarity of thought and action, and you are sure abt this opportunity, then there is no need to wait.
Either ways, keep all your receipts as most places allow for a certain amount of "pre-incorporation" expenses to be expensed. Talk to your accountant / auditor about it.
Wishing you the best!
