Having 6 credit cards will not decrease your credit score in and of itself. Your credit score is calculated based upon the following 5 factors:
1. 35% of the score is based on your payment history
2. 30% of the score is based on your total (all cards combined) credit debt to credit limit ratio
3. 15% of the score is based on the length of time you've had credit
4. 10% of the score is based on the number of recent inquiries on your report
5. 10% of the score is based on the mix of credit you currently have (different types is better than one type)
None of these things are directly linked to having six credit cards vs. one. However if you have six credit cards you need to be mindful of the above factors and keep your balances low compared to your total limits. Also, if you applied for all six at once that could temporarily hurt your score because of 6 recent credit inquiries that would yield.
I would recommend you focus on three which you can add over the course of a year. I have three and they are:
1. A MasterCard with rewards from my personal bank for emergencies
2. A Discover Card with a great gas rewards program
3. An American Express charge card which has lots of rewards and I use it for everyday expenses. Charge cards are different than credit cards because you must pay them off every month.
Hope that helps. You can browse all these card types at
http://www.studentplatinum.com