I don't think there's a right or a wrong time, age-wise, to have the 2nd baby. I think kids adapt and grow together no matter how far apart or close in age they are.
On deciding to go for it, we had to just fall back to before we had ONE and remember that even before we were married, we wanted two kids. So we figured it was as good a time as any!
The hardest part for me has been convincing my husband that we will survive the newborn stage. He had such a hard time with our son when we were all sleep-deprived and I think that really made him hesitate on wanting a second. But it's all worth it - we did it once, we can do it again! Good luck to you!