I've been developing non-ecommerce sites for years and I've learned is that CMS code/architecture quality, and the size of the community/ecosystem around the CMS are two essentials. For example, there are some smaller CMS's with great codebases that do very well in their specific niches. And WordPress is a perfect example of a very imperfect codebase and design, but it is supported by such a massive ecosystem of users, theme developers, plugin developers, installers and optimizers. It's hard not to find support for whatever you need.
I've worked on a couple of smaller ecommerce sites with Magento, OpenCart and some of the hosted solutions. Magento seemed overkill for the smaller site, but with a good ecosystem, and OpenCart was very light weight and it looked difficult to find off-the-shelf components for it.
There is an existing OpenCart install for this new site I'm working on - it has been configured and is working to some degree. I will not be the only developer working on this new site, but to get it off the ground it is 90% on me.
1) Which self-hosted LAMP stack ecommerce CMS should I choose for a new medium to large scale ecommerce site, and why?
2) Is OpenCart a strong enough foundation, both in terms of code quality and architecture, or should I go for Magento?
3) Or should I move away from what's familiar to me, and what's done already, to go to something else that is well architectured and coded and has a great following and ecosystem?
Your comments & suggestions would be greatly appreciated.