I realize it's probably too late to help you with your melons now, but I suspect the aphid damage has caused the yellowing of the leaves. Sometimes the aphids can spread a virus. Aphids are often attracted to plants that are fed alot of nitrogen, especially if you are using synthetic fertilizers. The new and juicy lush growth attracts them. Insecticidal soap helps to kill them and you can make your own.
The mold could be powdery mildew or downy mildew. There are homemade organic remedies you can make for pests and diseases. You should find these helpful.
Organic recipes for diseases:
Organic recipes for pests:
These sites have some good growing info that you might want to save.
Here's harvest info. Look at Muskmelon at the second site for melon harvest info.