ha は is pronounced as wa わ　only when used as a particle. Some words will use haは to be pronounced as wa わ　as well because the ha is being used as a particle. Those are very very rare though. Konbanwa こんばんは　is an example that will use haは.. I think only the greetings will use it that way.
Heへ is pronounced as eえ only when used as a particle. There isn't any words that will use he with the particle sound e.
Wo を is pronounced as o お because it is a particle and will only be used as a particle.
Everything is straightforward and those 3 are the only exceptions.
Sometimes the U in す、く、etc... will not be said, but that is up to the user (most likely be omitted). For instance, you'll notice in desu, the u is dropped and sounds more like des. Or with Yuusuke. It will sound like Yuuske. Another example is 好き　「すき」. It will sound like ski instead of suki. The u was dropped or rather, slurred. The slurring of words will be more noticeable as you become more familiar with the language.
http://www.guidetojapanese.org/learn/grammar
