Do not take both Step 2 CS and COMLEX Level 2 PE. Waste of money.
Ideally, you want to take this from April - August of your 4th year. Scores take 2 months to release. Most programs will interview you with it but they will NOT rank you post-interview until they see that you passed it. Therefore, the earlier the better because there's always a chance you may fail this exam and will need to retake it and will need to wait another 2 months for scores to come out.
You should be looking into scheduling and paying for this test as early as possible in third year. It costs around 1300. Don't forget about lodging and travel costs as well. You are paying 1300 for 6 hours of 12 SP encounters and a lunch.