I have had my current and first credit card for 15 months time to get a second?

Why? A second card will not build credit faster if that is what you are thinking. That 25% rule only applies if you carry a balance from month to month. You can spend all you want if you pay in full. What are you buying that $1200 isn't enough? Any second card will do the job, just be careful that you arenot spending your way into debt that you can't pay. Be in no rush to have debt.

It is always good to have a second card. Use them both, or rotate use. Either way, each is a back-up for the other. {Lost or stolen wallet, etc.} If you have a good, stable job (to better assure acceptance) go for a rewards card. Cash back is always good.

You are better off getting a debit card, so you don't start overspending. Use it for convenience, knowing you have enough money in the bank to pay. Life is easier when you don't worry about paying a bill.

No, one credit card should be all you need.