Credit Card Lounge

I’ve been getting quite a few credit card offers in the mail. I have gotten 2 MC in the last month. I also have a gas card, and two other MC/Visa. My question is? By opening these accounts, and not using them, am I improving my credit? BTW they are $0 annual fee. I currently rent, but plan on buying next year. Have no auto loans (2 loans paid off in the last 3 years 1 recently), however I do have a balance on the two existing CC. I currently have fair/OK credit. Thanks

In general I’m looking for U.S. numbers, but if you know these numbers for other countries, great.

other numbers I need:

- total # of auto loans made in a year
- total # of credit cards issued in a year