Good questions. It has taken much time for me to answer these types of questions myself. i consider myself a slave, but then only to the right person. It takes time to build a relationship, no matter what kind it is, D/s or not. Once you take the time to get to know someone, you begin to trust them (hopefully), they get to know what you like, don't like, and over time can and cannot handle.
As for your specific questions, i have given away email and website passwords, i've been pushed far beyond my comfort zone, i've had journaling daily about the most intimate thoughts and details of my life, i've come to the realization that if indeed i call myself a slave, and not a sub, that a slave in the end does not have the final word, and therefore i cannot without contradicting myself, have any hard limits. With that realization comes the fact that i am no longer in control, i have handed over control of my life to another person. i can give input on what i would or would not like, but in the end it is not my choice anymore. i see my sexual orientation as straight. If in the end, after i had my say, She still wanted forced bi, then okay. For me, being part of a slave is not just following the orders you want to follow, but following the orders you least want to follow. Lastly is the safe words, in the end safe words are there to protect you, both of you. If you have come to know and trust each other enough that you no longer need them, maybe. However some may argue that the safe secure and sane way to practice is always to use safe words.
For me it comes down to communication and trust. i will not give myself to another without absolutely and completely trusting them. Having the communication skills to work out issues, things that your having anxiety over and things that are making you uncomfortable helps tremendously. If you can trust your Domme to go to them with anything that is on your mind, anything that's bothering you, then the rest will fall into place easily.
End of rant
"Expect Nothing, Prepare for Anything"
Blake