Quality Content are good but you should take care that it shouldn't exceed your page need's. Over Content may boost Algorithm's to pose some negativity on both SE and user experience. A page of yours must not have more than 800-1000 words and that to all the words should be interrelated- Keeping in Mind The page load time.
Based on my experience with search engine optimization, i never think quality content will hurt page rank. Page rank will get hurt only, if you choose to do keyword stuffing. You may also get penalized for that. But not for having too much quality content.
Good quality content writing will never give you bad ranking. But you don't have to divert from the main theme of your site so as to gather more content.
What I would recommend you and this works. I did the same and it works very well. 1. On the first page make a general article well optimized for Search Engine(use h1, h2, h3 tags; use strong tags for your keyword; and alt tags for your images with your keyword)- in your case I would take Key Word "Canadian Moving Company" 2. From that page make links to internal pages to cities. In your case "Vancover Moving Company" etc. Do not put more than 30 links on that page. 3. On city pages put article about 700-1000 words. Keyword density use around 2% and optimize it same way I described on top. Do not forget to add 4-5 images with Alt tags. Its very important. URL for city links do in following format www.yoursite.ca/vancover-moving-company.html (those URLs works the best). All your keywords make in bold or strong. 4. Start building links to all those city pages with "Vancover Moving Company" pointing to each city. 5. What is not tested yet, but I guess it will play positive is a performance of the website. I would be able to provide with that information in 1-2 month. I just optimized the performance of all the pages, and they are not crawled yet. I have same system but different business. If you want to see an example and SERPs for that, PM me.
For optimal use of Alt Tags, should the images be stored on the site hosting account or is it okay to store them on 3rd party servers/sites like that of imageshack.us ? Hosting on 3rd party servers might be helping the 3rd party server in generating traffic and not the site where the image is posted - but I am not sure.
i don't think that quality content hurt your ranking yet it is used to build up your ranking and overdoing is not the issue but i suggest you to keep it the content much compact and more interesting.
Keep your web pages content not more than 500 words. Else the robots/crawlers will not read them. So the content beyond 500 words in one page will be in vain. Instead you can use this excess content to create new pages, it means more SERP. PS SEO related queries generally needs more detailed explanation though.
Keyword stuffing is not quality content... But you can never have tooo much quality content! You can never have too much great writing!
"Quality contents" are ok, but "(too) optimized contents" are not. And I don't think having other pages with different theme with your main one will hurt, but if they have the same theme it'll surely helps though.