marketpress and wordpress usability - too many options for store admin

Ive been testing marketpress for a week now. I love it form a superadmin point of view, but I am frustrated by the number of options store owners/site admins have. They have full admin access to the wordpress dashboard, which means they can add users etc and access other options which I would rather keep hidden as they can potentially mess up the store settings by deleting files, adding sites etc.

Even though its possible to switch of their ability to edit plugins, some plugins install menu options which all admins have access to.

Ive tried several plugins to hide the menu items, but these just "hide" the menu items. Anyone with any basic wordpress knowledge can input the link directly to get to any of the admin menus.

Also in the marketpress settings some of the store owners options could be made optional. I think I read that this was a plan for future releases. It would be nice to have the option to switch off html editing in posts. Also the image upload process is too complicated for the store owners

Ive asked a couple of people to register stores and experiment with adding products and they all failed to properly manage their images. Either forgetting to add a feature image, or achieving ugly formatting in their posts. These are people with no blogging experience - used to sites with simpler interfaces like etsy, ebay etc

My goal is to make a site that has my brand and look over all the stores, but with options to add custom header images and a few other minor options. This is possible with marketpress but the wordpress admin/dashboard makes it harder to achieve this without lots of plugins and hacks. I am wondering if I should keep going down the open source route (preferable, but frustrating) or admit defeat and look at the readymade (expensive) commercial options.

Has anyone set up a wordpress store with a user friendly setup for store admins? What plugins did you use to achieve this?