mrod said:

Those commissions vary frequently due to experience, financing approval, etc. Should the sales people be added as employees (with no deductions) or vendors?

That depends on whether you will be issuing a T4, a T4A, or whether the sales people are employees of another company and you're receiving an invoice.   CRA rules tend to lean toward everyone who works for you being an employee unless you prove otherwise.   If they don't have their own tax and WCB numbers, they're probably considered employees.  See the CRA website for more information.

mrod said:

As well, our payroll is entirely handled by an outside company. Is it necessary to input historical payroll data? Should I put payroll expenses as a vendor as well?

No, when setting up history you can put in a balance, but if you're using 2009 you wouldn't be using the payroll module so you couldn't be printing T-slips, and it doesn't matter what data is recorded in the Payroll ledgers.  Transactions entered will posts through to the G/L, but the calculations are shut off.

The salespeople are independent contractors. They are all self employed.