Good questions. Being a switch can be... complicated business. Fun, rewarding, but complicated.

-Do you feel the urge to dom and sub a single person at the same time? Maybe at different times during the same scene?
Short answer, yes. In fact myself and my woman have a particular scene that is very close to our hearts that incorporates this very idea, in which I start as the sub, I move to a Dominant role, and in the end I return to my role again as a sub. This is not a constant thing, but there are times when it certainly fits for us. There are many occasions when we do not do this of course, but sometimes we do.

-Do you dom and sub at the same time, but with different partners
I'm only in the one D/s relationship. I could see doing it, in theory. But I have not, to this point, been in two seperate D/s relationships where I've held a different role in each at the same time. I'm not... personally prepared to dedicate myself to two people on that level. At least not right now.

-Do you take turns with your partner (tonight, I'll be the boss, tomorrow night, you be the boss)?
For us it's very much based off the "feel" of the moment. We read each other well and more or less think along similar lines so it makes that workable for us. I can see the advantage (as well as the attraction to the needed discipline) of more "scheduled" switching however.

-Do you feel like a dom/sub for long periods of time, then feel the need to switch again (i.e. feeling like being the sub for weeks/months/years then kind of feeling dom-my for awhile)?
For me yes. I am a sub the majority of the time, with what I call "bursts of dominance". I tried being a full-time Dom and it becomes mentally stressful for me after a time. For me a balance where I sub more than I Dom is preferable. My woman is the other way, she is mainly a Domme, and a very good one, and with me she is exploring the feeling of submission on occasion. Overall this balance, combined with the solid friendship we have, works very well for us.