The problems with the images got noting to do with MarvikShop, but with your server directories parameters.
There are several possibilities to show the pictures. To help looking why the picture was not set, get the image info with the right mouse button. So you can see what link it should be. The easiest one for you is the one Sandra makes. Just put the picturelink in the product info from you catalogtab from MarvikShop in the admin.