OOPS! I laughed! Sorry ;P

If you don't mind, there are some corrections to be made with the pronunciations you wrote in the brackets/paranthesis.

1. おはよう！（o ha yo u) - good morning [It's perfect!]

2. こんにちは！（ko nn ni chi ha) - good afternoon  [3 'n's are not necessary when writing in English since it would also change the way it should sound. Two 'n's are OK. More importantly, the "は" is pronounced "WA" <em>NOT </em>"HA". This is one of those exceptions that you don't see coming, like watashi WA kyoshi desu (私は教師です). So, altogether it will be: Konnichiwa] 

3. こんばんは！（ko nn ba nn ha) - good evening [The same rules apply here too, so I am guessing I don't need to explain this one ;). Altogether it's: Konbanwa. However, as a foreign person, I realized (which the native Japanese speakers won't often realize) that the way they say it, it sounds more like "Kom-bang-wa" rather than "Kon-ban-wa". Please keep in mind that foreigners learning Japanese must acquire the fact that the "ん" has about 3 sounds: "n", "m" and "ng".]

New phrase

良い夢をー　（yo i yu me wo) - sweet dreams
（よいゆめを）

If it's not too much for you, I would like to teach you another new phrase just like 良い夢をー that one of my good friend taught me when I started learning Japanese last year. ”よいいちにちを”. It means "Have a good day". Easy to remember, right?!

がんばってね。 ^_^