What is important to consider while building an adverbial phrase?
It seems that you like rules, but soon you'll find that exceptions are the norm. Don't consider the following as rules. They are just examples.
How to put them together?
It is indeed very flexible, as it is in English:

轻轻的我走了。 Quietly I left.
我轻轻的走了。 I quietly left.
我走了，轻轻的。 I left quietly.

The 2nd is the most common form, but the other two forms give the sentences a poetic touch.
Notice in the last example you put a comma before the adverb, because Chinese is mostly a left branching language. This is how you make a right branch feel natural.
[rant]Someone may want to criticize my use of 的 and say that I should use 地 or 得 instead. In fact 的地得 is totally indistinguishable in speech, why bother distinguishing them in writing? My example is from the famous romantic poet 徐志摩. I'll listen to you if you write something better than him. Also stop being a grammar communist OK? [/rant]
There is another form of positioning, V + 得 + adverb:

跑得快，有糖吃；跑得慢，没糖吃。
Run fast and you get candy; run slow and you get candy wrappers.

How long and how complex can it be?
As long as you like. This is how you stick many adverbs together:

我非常非常非常非常非常非常非常非常非常非常非常非常(gasp)非常非常非常非常非常非常非常非常非常非常非常(gasp)非常非常非常非常非常非常非常非常非常喜欢你。

This looks like cheating, but you can have this:

我们要以十八大提出的解放思想、实事求是、与时俱进、求真务实的精神办好这件事情。
We should complete the task with the spirits of the Eighteenth National People's Congress meeting, which includes liberation of the mind, faithfulness to the truth, advancement with the times, and emphasis on pragmatism.

Still this is but one colossal adverb phrase, not exactly &quot;many&quot; phrases.
How to do more than one adverb phrase?
From 阿桑's song (who died of breast cancer in 2009):

你听寂寞在唱歌，轻轻的，狠狠的。
Listen you to the loneliness singing, quietly and ruthlessly.

Here is another example, with three adverbial phrases:

乌龟又慢又稳地，一步一步地爬到了树顶上。
Slowly but surely, step by step, the turtle climbed up to the treetop.