EVA Monk

Ive seen this player that stack bloodfight, forgot to take a note though

So, whats the cap for eva?
and is it a good thing?

I cannot answer your first question. However, it would be easy enough to find the cap on evasion rate by pulling a horde of lv.1 mobs and parsing their laughable attempts to defeat you.

As for your second, you can find a discussion on monk as a tank (inferred from EVA monk) in this thread.

The abbreviated version is: two other jobs can tank better, and to shoehorn monk into the role of tank is to ignore monk's strengths.

I will say though, if you get a large amount of evasion you will notice it when soloing off similar-leveled enemies so it's worth looking into when making a soloing set.