This website should hopefully help you out on assignments 4 and 5, as well as provide some ideas for your final projects.
Photoshop has many different gradient options, that are a lot of fun to play with. I highly suggest looking through their preset gradients, as well as perhaps making a few of your own.
To get to the gradient menu, go to IMAGE --> ADJUSTMENTS --> GRADIENT MAP.
The following menu appears, with several gradient choices. Clicking on the long bar will open a larger menu, which allows you to create your own gradients and color combinations.
The following are examples of some of the different gradient options, applied to a picture of cupcakes.
The Threshold tool allows you to alter the amount of whiteness and blackness in each image. It measures the levels of darkness in the image, and by changing those levels, the image can look dramatically different.
Some examples of the different levels are: