If a defender uses evasion in response to being attacked, does the attacker get to ready since there is no longer a legal attacker??? Thanks alot!

Also when you replace a character that is exausted during the build phase, does the new character come into play ready or exausted??

Yes. But, the reason is because the defender was removed from the attack, if the attacker had been removed then the Attacker does not ready (unless a card specifically allows him to like Betrayal of Trust)

what if you playa plot twist to move the position of a defender making him protected and the attacker does not have flight, does that negate the attack and make the attacker ready??

it would not negate the attack, the way you have it written but there's a couple of important distinctions to make.

you must propose a legal attack before you actually attack then you must pass, then your opponent can play effects. Then your opponent passes, then you pass again. So if your opponent does something to invalidate your attack before the attack is actually under way that's fine then you would just propose another legal attack. If the attack is allowed to go through without your opponent invalidating it he could move that thing from here to Timbuktu and the attack is still valid.

Thats really confuising!! why would the attack go through without the opponet playing the card to move his position in the first place? IS it only if they are dumb and forgot or not realize to do it that them moving them would the negate the attack?

There could be lots of reasons for a hypothetical opponent not to move the character perhaps they have a way to stonewall the attack. It's really not that confusing once you get the hang of it, just remember that when you have the priority you can do as many things as you want, but you must eventually pass the priority over to your opponent. So take Attacking for example.

You: Propose Attack with Character A into Character X, Pass
Her: Plays Effect Invalidating attack, Passes.
You: Plays Flying Kick, Proposes Attack, Passes
Her: Passes

At this point you've both passed and the game moves on to the next step your character exhausts and gains the attacker characteristic, her character gains the defender characteristic, you have the priority, now you can play more effects or you can pass. If you pass and she passes then you move on to the next sub step which would be attack resolution.

As far as I'm aware you can only propose an attack when the chain is empty. Both players will need to pass after flying kick to allow it to resolve
before an attack can be declared.

(otherwise when its your initiative against titans the smartest response to them trying to stun one of your dudes with roy would be to declare an attack with them!)

Yes, of course, he just skipped a couple passes to condense the example.

To recap on the OP's questions, if an attack has already been declared legal and the attacker has exhausted, then if the defender evades, the attacker does ready.

I'm not sure exactly what you mean by "replace" a character... if you're referring to recruiting another unique character with the same name, then it just comes into play normally, and the existing copy is put into your KO'd pile. It doesn't matter what the existing qualities and states of the original copy are.

However, if you're referring to substituting a character, keep in mind that you must remove a ready character you control from the game. You can't substitute out an exhausted character.

I'm not entirely sure what you are having trouble with, but maybe some of this will help:

Situation 1: You have two characters in your front row. I propose an attack on one of them with a character who has no flight or range. In response, you say that the attack is not legal and play a plot twist that moves the proposed defender behind your other character. The attack never happened, and I now need to play something like Flying Kick if I want to attack that character.

Situation 2: Same basic situation, but this time you declare the attack legal, and my character exhausts. You play that same plot twist, moving your defender behind the other character. You may have a good reason for doing this (e.g., an effect that gives him reinforcement when he is protected), but doing so does not negate the attack. The legality of the attack is checked only at the time it is proposed. Once it is accepted as a legal attack, no changes in position by the defender will negate the attack. (For example, if I propose an attack on your Alaris, you can declare the attack legal, then pay 2 endurance to have him switch places with a character in your hidden area. The attack will still proceed to conclusion, even though the defender is now in your hidden area.)

Situation 3: Same basic situation as in 2. The attack has been declared legal. I play two copies of Big Leagues, boosting my attack by +8. You play Spider-Sense Tingling! to give your defending character evasion and then you evade him. My attacker would re-ready, but my attack pumps would be wasted, since they lasted only for the one attack.