I`ve found Yamaha website and noticed there have 200 series (Student Model), 300, 400 series (intermediate Model), 500 up series (Professional Model). Could anyone know what`s the difference and if I buy a student Model from the beginning, how long after I should buy intermediate Model and Professional Model?

Thanks!

Generally speaking:

200 means the body and keys are cupro-nickel alloy, silver plated.
300 means the flute has a sterling silver head.
400 means it has a sterling silver body.
Higher models may have sterling silver keys as well, or gold, or may be "hand made", may have soldered tone holes.

However there are a few exceptions to this pattern.

There are also many other minor details, such as the type of pivot screw.

What is REALLY important are the intricate details of acoustic design, which are not listed. The high model flutes do not play better because of the materials, or the screws or springs, but probably because of slight differences and care over acoustic design, such as the precise shape of the embouchure hole.

There are quite a number of Yamaha websites. Did you find this INFORMATIVE one:
http://www.yamaha.co.jp/english/product/winds/index.htm