My question to you - why do you want to blog about candles? Is this as a hobby, passion, or is this a method of bringing in customers to ecommerce site. You have to look at your goals for blogging - branding? Customer acquisition? Positioning yourself in the industry as an expert?
If customer acquisition is important to you, I'd recommend building the blog on the site itself, in a folder called /blog - this way, as an expert in your niche, you've positioned yourself in that manner, and people will want to buy from you due to your expertise.
From an SEO perspective, your high quality blog should naturally gain links, and can certainly be promoted through outreach and gather links in that way. This will help your ecommerce site's visibility and reach in the search engines, and will strengthen the domain as a whole. You don't get this if you blog offsite on a different domain - you won't be gaining this link strength for your site, which should be an important consideration.
Mark