do i need evasion (in General)

i have a DD Toa fireball mage, should i invest to evasion, if so when or how much

You have ToE, not ToA lol. HUGE difference (ToA would be a waste)

I think you should get at least some. Don't expect to be able to out-match ToA teams, just know that eventually a minor investment will be enough to eliminate one whole blow from the enemy. That may turn out to be a whole nother round of life, and in turn, one more amazing blast of FB.

I would suggest using Evasion, and keeping it between half and 2/3 of your HP level. That's what I did back when I was just a SFBM, and it worked quite effectively.

You're going to need to train enough to keep people from hitting you in ranged, without losing too much DD or HP. The big boys seem to have evasion trained to a little more than half of HP, with DD being more than double HP.

oh ok sounds like dm and evasion should be around same # then ?

i use little +51 DB's with a AOI (both rented) to enhance evasion is this sound ?

Depends on the level you are playing at. +50s are peanuts at the higher levels and killers at the lower levels.