Well no as evasion implies that tax isn't being paid at all.
Avoidance implies that you're avoiding paying all of your tax but you're still paying some tax.
No it doesn't. Even Al Capone paid some tax. The difference between evasion and avoidance is whether or not you can prosecuted for it with enough chance of a conviction for the authorities to take you to court. A skilled accountant can make the difference between the two. Even just hiding the evidence well enough takes it from evasion to avoidance.
The words have pretty much the same meaning. For example, I just did a search for "evade". Just the word, nothing else:
https://duckduckgo.com/?q=evade&ia=meanings
The second hit was a thesaurus:
http://www.thesaurus.com/browse/evade
And, unsurprisingly, "avoid" is listed as a synonym for "evade".