For all your four questions,the short answer is yes. But notice,小时is more formal.For instance,you always find a 小时 in newspapers,or CCTV News. Besides I think if you say 一个钟 to people who don't speak Cantonese,he MAY not understand you.Or he may,that depends. Certainly if you say 一个钟头, people know what you mean.

they are some things

1 yes, but usually used in spoken Mandarin 2 yes, they have the same meaning 3 yes 4 yes

我觉得除中国部分南方地区如广东、广西、澳门、香港等会用外，其他地方的人都不会用。而且还或许不知道你说什么

大家朋友，谢谢你们，现在明白了。