Is the Spanish guitar the same as the Classical guitar?

No, scales and sounds are different from eachother. ther is spanish classical guitar as there is classical guitar for any other part of the world as well.

When we say classical guitar, it usually means guitar with three steel string and three nylon string. Acoustic guitar has six steel string.

Yes. As long as the tuning is the same. EADGBE is standard tuning on both electric and classical guitar, but there are varities on this. Follow the link in the related links section to teach...

The term acoustic guitar in general do not refer to classical guitar. A typical guitar has narrower neck and steel string, classical guitar has wider neck and nylon string

No. A classical uses nylon strings that are softer than the steel strings found on an acoustic. The acoustic produces a brighter, sharper sound.