A very helpful book i found called "Japanese the Manga way" explains this as there being 4 different levels of politeness. おはよう on its own corresponds to a level 2 politeness, between friends. Adding the ございます bumps it up to level 3, normal accepted politeness. So, for people you have just met, don't know, or superiors.
Close. The extra う at the end signifies that the last syllable has a long vowel instead of a short one and so must be pronounced with twice as much time as most other vowels. So something like "o-ha-yooo".
In Japanese, how long a time you pronounce certain sounds does change the meaning of the words. There is this thing called the long vowel, which in Hirigana is denoted with any character--except ん of course--followed by a vowel kana of the same (or at least similar in two specific cases) vowel; in Katakana, the second kana is replaced with a ー.
Syllables in Japanese tend to go by very, very fast, and yet these long vowels can make one syllable last as long as two. Japanese double consonants have a similar effect by lengthening the consonant instead of the vowel, but that's a topic for another day.
For more info here is this blog post: http://www.guidetojapanese.org/blog/2008/07/11/explaining-the-long-vowel-sound/
は is the hiragana "ha" used when writing words with a "ha" sound
- おはよう - "ohayou" good morning
わ is the hiragana "wa" used when writing words with a "wa" sound
- 川・かわ "kawa" river
は is pronounced "wa" only when used as a particle; this particle marks the topic, which is the overall theme/contextual information for a sentence.
- こんにちは "konnichiwa" hello -「今 kon "now" 日 nichi "day" は wa (topic marker)」lit. "on the topic of today..."