All Things Numbers

Since there are multiple ways of saying the same numbers (i.e. stuff with　よん/　し、 なな / しちand きゅう / く ) I'd like to know which one's are more, let's say, appropriate. For example I'd like to know if it's better to say にせんよんねん or にせんしねん.

Ignoring dialect (for the most part), which ways of saying a specific number may be correct but sound really weird? This question isn't supposed to be limited to straight counting from 0 to x or using dates but is meant to incorporate all things involving numbers you can think of,
If there's a certain context that makes one better than the other in a specific situation, if you usually use one but use the other to emphasize sth, if one's just more common, if one would be theoretically okay but sounds weird (kinda weird - pretty weird - really weird, etc.), if both are fine, if there's a general rule of thumb, and so on, I'd like to know about it. Just throw in everything you can think of.

Thanks.

Both are incorrect. You should say にせんよねん.
There is not simple rules/regulations, I believe. (I'm a native speaker.) Just experience and remember.

This is the standard way how to call numbers.

http://www.sf.airnet.ne.jp/ts/language/number/japanesej.html

200 Ni-hyaku
300 not San-hyaku but San-byaku
400 not Shi-hyaku but Yon-hyaku
500 Go-hyaku
600 not Roku-hyaku but Rop-hyaku
700 Nana-hyaku
800 not Hachi-hyaku but Hap-pyaku
900 not Ku-hyaku but Kyuu-hyaku

0 usually not use rei but zero(though it is english)

Please don't be confused.

When lauching the rocket, the coutdown in Japan,
Roku goh yon san nii ichi zero(not rei).

My bad friend ask me, "Do you know why he use zero not rei in japan on the coutdown".

He said, "It is because",
if he says rei on the coutdown,
the rocket should bend its head in Japan."

My bad friend ask me, "Do you know why he use zero not rei in japan on the coutdown".

He said, "It is because",
if he says rei on the coutdown,
the rocket should bend its head in Japan."

Ahahaha. That's a good one (joke/pun) right there!

If your textbook does not cover at least the most common patterns and exceptions, throw it in the nearest recycle bin and get a new one.