>Do I need an accountant?
Need? No. Good idea? That depends on how much money you're bringing in, what type of work you do, and what your family situation is. If you're married and/or have kids and want to put one of them on the payroll, or anything like that, then an accountant's a good idea. If it's just you doing business yourself, then probably not.
>Is it necessary to keep track of every receipt including transportation, gas, food, etc.?
It's necessary to keep track of what you plan on claiming as a business expense. If the CRA decides to take a look, it helps to have the paperwork.
Whether you incorporate or not, here are two recommendations.
First, get a credit card dedicated for company use only. That way the banks will be provide all the tracking of your company's cash flow. Pay for it from the corporate (or sole proprietor) bank account. Do not mix your personal and business accounts, ever.
Second, pick up a decent scanner. I got a Doxie years ago (they don't make my model anymore, it was an earlier version of this), and I got in the habit of scanning every receipt, which made the accounting a lot easier, and justified expenses.
>What are the benefits compared to an employee?
You get to write off stuff that you buy for work, but be prepared to justify it. If you do software development, for example, then your computer, printer, monitor, scanner, etc. can be written off as a business expense. If you go on site to support customers, you can write off a percentage of your car expense as business, etc.