Rather than proposing a solution to the whole project, I propose a solution to the editing problem you encounter — the problem that cripples most templates and that will cost the most in your project — the problem that most of your designers will not be able to solve except at great expense. I have created the free TagBot template-automating program that is available for Windows or as an online tool, and that is used by many eBay template designers to simplify user-editing of their templates.
After you find the template you want, my bid is to TagBot that template so that it can be used in your choice of online or desktop TagBot tool. The tool will display slots for only that portion of the code that is to be changed, so there will be slots for photo URLs, slots for changing text, attribute options, and blocks that can be checkmarked for inclusion or not. Google "tagbot templates".
To use this method, your template content should be reasonably standardized (the purpose of using a template in the first place). That which will change with each item should also have a constant format so that you can generate your description as plain text and have it display correctly after insertion into the template slot. Depending on your template design, you may also be able to insert blocks of text from a web-authoring tool.
Many users request tagbotting so their 10 year old daughters or 70 year old grandmothers may safely and easily add product content to a listing template.