The guitar salesman in the shop I went to, advised me to buy a classical guitar with a nylon string to start with. What do you think about that?

I don’t agree at all.

Classical guitars have much bigger necks compared to acoustic guitars or electric guitars and they are too hard for the beginners to practice with.

I would suggest you get an acoustic guitar or acoustic electric guitar and put light strings on it. You will find it much easier to practice with.