My reading is that a grapple works as a block on all actions, including defensive ones, until it is broken, once you do break free the block on actions no longer affects you. Remember that blocks don't prevent actions being attempted, they just make them more difficult to accomplish. If you roll high enough to beat the grapple you break the hold - depending on the kind of action you're taking and specifically whether it's logical that it would directly break the grapple. In the case of dodging the physical movement should be enough justification to break a grapple if the roll is successful. The value of the Grapple is not taken off the roll before it's applied to defence, it's just that if you roll higher than the result you need to dodge, but less than the value you'd need to break the grapple, you'd fail to dodge because of the grapple pinning you in place. Conversely, I think if you roll higher than the grapple value, but not enough to dodge, then you successfully break the grapple, but still get hit by whatever you were trying to dodge - I may be wrong on that last but though, I don't have the rulebook to hand.

First of all: welcome to the forums.

Regarding 1) In my opinion everything depends on what kind of ritual you are speaking of. This is far to diverse to answer with a singular ruling. If the ritual is a fairly common one like the tracking divinations Harry usually uses and the wizard knows them very well then you don't have to go through all the preparations (most times the lore skill combined with one or two declarations would suffice here anyways).

If it is a more complex ritual like the entropy curse then yes. The preparations have to be done every time. You have to understand that the preparations are not only of scholastic nature, there are many many other components. Ingredients might get used up or tainted by magical energies during the ritual and have to be replaced before the next one. You might have to get your mind prepared though meditation before doing it again. These are many things that are mostly done as declarations... You don't have to play them out every time. Just make a uber declaration like in the rules and be done with it. When the caster of a ritual isn't in a hurry, then you can skip the casting all together. Given enough time any ritual will go through without a problem...

Regarding 2) Nobody can prevent the defense roll. By the rules if you are attacked, you can try to defend against it. As a GM you are within your right to compel an aspect of a player in the way that he is not able to defend because of an aspect that you as the GM place on him during the grapple, but thats really all you can do. If the player decides not to take your fate point and buys out of the compel, then you have to let him defend it. It comes down to narration at this point. Example: If you have someone in a headlock he still might be able to dodge a swing of a sword somehow or go limp and drag his grappler to the ground evading the gun shot.
Sometimes it makes no sense. I agree with that. It comes down on how the grapple is described and what you as a group deem reasonable... 

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Does the caster need to do it just once for a given ritual, or every time they want to cast the spell?


every time.


a real nasty ritualist inflicts the consequences on others - blood sacrifice, mental abuse and the like. if they do their sacrifices on a single victim they could get up to 12 (the consequences) + the stress bar out of it. have multiple sacrifices and you can power up a hell of a spell. (have your nasty a coven or sect with several willing subjects, and you can power a spell while the last sacrifice subject recovers.)

don't forget, that a caster can 'skip a scene' to gain shifts for complexity or he invokes aspects and/or and makes declarations.

uhm, papa gruff was faster...