Manequins

From kerning subway you take it to ximending then on the left there's an Npc that takes you there.
I personally went there starting lv70 as a white knight, however they have high avoid and they hit really hard. Exp definitely pays off since I got more exp than leeching.

 

Not sure, you'll have to experiment yourself.

 

According to the ML website Male Mannequin is level 80 and has 45 avoid.
If you use the acc calculator ( http://screamingstatue.com/accuracymain.php ) it will tell that you need 230 acc at level 70 / 165 acc at level 80 to hit 100% of the time
Not sure how reliable is this

 

With 145 accuracy you can hit Kid Mannequins(Level 75, 37 avoid) 100% of the time at level 74.

Not sure if you're using any potions to get that number. With a Sniper Pill you can 100% hit them at level 72. With an Amorian Basket you can hit 100% at level 66.

How much accuracy did the 3rd anniversary candies give? 20? Well with 165 accuracy you'll need to be level 70 to 100% hit.