You can have more than one mod installed at the same time, as long as they don't involve the same game images. For example, you can't use 2 different flower mods (like the purple roses and the fruits & veggies), because the images from one mod will replace the images from the other mod. The best way to check is to look at the names of the image files in each mod to see if they are the same or different. If they are the same, one mod will replace the other one.