What is the t* for n=18, alpha = .05 for a one-tailed test lower?

What is the t* for n=18, alpha =.05 for a 2-tailed test?

If the |z| < |z*| the decision is to reject the null, would this be a fair statement or not?

If the p < alpha, the decision is to reject the null - is this correct?

If we reject the null hypothesis, we conclude:

There is sufficient evidence to indicate that the null hypothesis is true Is this correct or not?

If the population standard deviation is known, we use z Is this correct or not?

If the sample standard deviation is known, we use z, Is this correct or not?