As to magic, when drawing down power do you need to roll, or do you just draw down a level equal to the relevant skill, whatever that skill is?

Once you have drawn down the power I believe you roll your control. Do you need to get a score above the power level to control it? if you don’t, I presume it spills out and has unforseen effects, and may do the caster damage?

With a stress inducing spell, does it do the power level in stress points, or the level of control you have, or something else?

Does using a specific created foci (ritual knife, blasting rod, staff, etc) decrease the difficulty of controlling magical forces and how does it do so?

The game advises you to start from the most practical point possible – that being, an NPC and their motivations – and work your way back from there. I think it works out pretty well, especially if you take all the other advice in the GM chapter about making rolls interesting and whatnot. What it comes down to is this: who is your NPC, what do they want, how do they go about it, and how far along have they gotten before the PCs get introduced to the situation? The further along they are, the more clues there are to distribute.