It doesn't really "affect" credit, but it establishes credit. For instance, if you go to your bank and borrow $12,000, and depending on your interest rate, and how many years you finance it, you make your monthlys to the bank. When the bank and other creditors see that you can responsibly pay your bills on time, that is how you establish credit. So later on in life when you want to go out and get a C5 or a C6, they will review your credit report and say hey, this guy was never late on his payments, so let's give him a loan for that C6. Having a loan with a bank will also help you when you want to finance a home, or get a major credit card. See, the bank has an interest in loaning you money. Number 1, if you don't pay, they are going to have a nice C3 to sell and re-coup their loss. Number 2, they are making a little money off of you because of interest. If your father has good credit, he can co-sign for you which would get you a lower interest rate, which means lower payments! You must understand though, if you have a co-signer and you flake on payments, they will hit up your dad for payment.
The only way your credit can be "affected", is if you don't pay your bills. Bad marks, at least in CA, stay on your credit report for years, and you can be taken to court and have a judgment entered against you for an unpaid debt, or even have your wages garnished.
It might be worth looking into, at least to see what your monthlys would be. You may be pleasantly surprised, especially if you have down payment to put toward the vehicle. That will make your payments lower too.
I don't know your age or what you do for a living, but taking on a small car payment can be good for you in the long run, as long as you are responsible in paying. If you have a checking account with the bank that does the financing, you can set up direct payment. That means the bank would automatically withdraw the money from your account. This is handy because there will never be a late payment, unless of course there are no funds to take.
I financed my C3 for 3 years, and my payments are a hair above $200/mo. Quite manageable for me. Check it out TR, it certainly wouldn't hurt. You never know, you may have that beautiful C3 in your driveway next week! Remember though, to not over extend yourself financially. Your dad will help you in making that judgment call.
BTW, I don't blame you on the manual transmission. I had to learn to drive a stick when I got my car. I just was not going to own an automatic vette. It is a beautiful car though, so weigh your options, and I wish you the best of luck in your decision making.