I think that the customs option is higher urgency than scoping out the Cathedral just now. It is certainly next on our list. I think we've already got astral surveillance, and a little matrix surveillance. We need eyes on to try to suss out their physical security. The problem is that they are already aware of us and quite possibly what we look like and maybe our SINs. The customs thing is only likely to work because our appearance will be disguised and the Sisterhood doesn't own customs, and so they aren't likely to be clued into us. Splitting the party and sending them in close to the heart of the beast seems risky - better to do the surveillance as a team and with stealth and deception.