I know it seems really overwhelming, but don’t worry about Step 1 yet. What you can be doing at this point is to pick up a copy of First Aid or Step Up and start reading it and annotating it with your own notes. (If and when you have time.) If you use it to study with as you go along, you’ll be more familiar with it when crunch time arrives.
The Kaplan Q-Bank may be offered to your school at a group rate, so just sort of sit on that one. We were offered 1 month and 3 month packages; I opted for the 3 month, but did practically all of it in the last month.
This summer, you can review if you want to, but I don’t know how much it will help you. A great deal of Step 1 is covered in Pathology and Pharmacology, which many schools don’t get to until 2nd year. Take the summer instead to earn some credits towards your fourth year (usually via service learning, spanish classes, or something fun.) Oh, and try to get away for awhile- it’s your last true summer with no obligations, so enjoy it!