just to add my 0.02c on the subject:

My personal opinion is that in most relationships, even non BDSM ones, couples end up knowing each others passords to things in time, it is simply a point of practicality that sometimes one of you has an amazon account and the other wants to order something, it happens.

In terms of a BDSM relationship would I ask for a password just for the sake of having that little bit of control? No probably not, do I know my slaves passwords for things? Yes, but for the reasons detailed above. Would I expect her to give me a password if I wanted it? Yes I would.

Onto the other things you mentioned I think safe words is a grey area, for most they are essential, in practise I think once you know you master well, and he knows you well, he knows what you are and aren't capable of, and as a result, even if the safe word exists, it may never get used.

Sexual orientation is a funny one, I have heard slaves say that they are straight but would perform homosexual acts for their master, however I am not sure in the real world how far this can be forced, and never something I have experienced or had to deal with, having only ever had bisexual subs (through sheer luck!)

The reference you make to a collar is an interesting one and fairly impossible to give a generic answer on simply because a collar means different things to different people, for some it is the end of freedom and privacy (as most slaves would see it), to a sub it may not involve complete end of freedom, and online a collar more often ends up just meaning play partner.

Should hard limits be pushed? Yes, in my opinion, but depending on what the hard limit is, if it is something like a phobia, then it is probably best left alone, if it is something that came from a traumatic experience, probably also best to leave alone. If it is something the sub simply doesn't like, and the dom does, then perhaps there is some room for pushing there.

Regards,

Arch