I went through this and can help you with the information. You can work full time ( 40 hours or greater than 20 hours/week) during summer. Since , you are graduating in the fall 2014, and if you are taking less than 9 credits, you still can work full time (greater than 20 hours/week). You need to get done with the college work before you start working. Get approval from the department dean, and make sure , the work area field is related with your major.
Cpt can be full time and part time, Full time during breaks or when school is not in session and part time when school is in session.
Part time CPT doesn't affect your OPT but more than 12 months of full time of CPT will void your OPT. So, make sure, you wont be working more than 12 months of full time CPT. Since you are graduating this december and if you are taking less than 9 credits this fall, you can work full time until december. And , you can file opt on september and again start working with the same company after you graduate under OPT.

Let me know if you need more information. I have one blog regarding this CPT info as well. You might want to check that as well.

Good Luck.