Mandarin Chinese pronunciation (pinyin)?

Hi, I have a number of questions about Mandarin pinyin pronunciation:

1. How do you know when "i" in pinyin should be pronounced "uh" or "ee" or "er" as in the English word "fur" (examples of usage in chi and shi)? I've heard it as all these ways and am very confused as to which is correct, keeping in mind I am aiming for the Beijing accent.

2. In the pinyin "e", how does one know if it is to be pronounced as the English sound "uh" or "eh"? I have heard "ye" as both "yeh" and "yuh".

3. Does it really make a huge difference if you give your "ch" and "zh" different forces of air, like I know some of the sounds have more air than others, like "p" and "b"...?

4. Which region's/city's accent is the most understood throughout the PRC?

5. "Eng"- pronounced like "ung" or "ang" in the english word "hang"? How do I know which is right? Like for example, cheng2 chi2

I know that if I heard the word before I should know how to spell it in pinyin the problem is I'm hearing so many different ways to say things! Please help! Xie Xie!!
So are there exceptions to the pinyin "e"? Such as in "de" in "wo de"? Isn't that pronounced "duh"?

Thanks for the info on pronunciation variations though...I'm sure it's similar to Spanish, with Castilians having a lisp and the Argentines with their pronunciation of "ll".

Is there a translation site or software that will translates Chinese pinyin to English?

Thank you for the suggestion, however, I have tried Bablefish and others. They allow me to only translate from Chinese simple or traditional to English.
For example,
If i try to translate a simple word as "xie xie", it does not recognize these word.
Thank you, however, I really
I'm looking for a translator that I can use online to translate Pinyin to English and English to Pinyin. I already use Babel Fish Translation for Chinese to English and English to Chinese. Need a Pinyin to English is the primary need