Focus questions, sustained focus and odd weapon focus Options

[Sokei]

I have a character that wants to use a sustaining focus from char gen , which i don't mind but as i read the description neither one of us could find the answers to some questions we had:

1. when does it shut off (if at all)
2. he seems to think that mages can focus spells at the focus (im pretty sure this isn't right , but i could be wrong)
3. does he have to cast the spell into the focus beyond the first time.

the other question , he has 1 arm that is cybertech which goes with his character background. he wants to make his cyber claws in his right arm into weapon foci... i personally don't think this will work but he insists, and i don't have an issue with him having them if they can even be made like that. so my question is , can cyberweapons be foci ? and if so would they cost more, and could he even use them in astral space because he has no arm and cyberware has no astral signature the foci would float next to him im assuming but wouldn't function ?

this could very well be a dead horse and i apologize if so :grinbig: any help is appreciated greatly.