Look at it this way; the simulator is meant to be simulating a car + ELM327. Basically, it simulates everything you need to do this work.
So, yes. You can ask it for RPM and speed, and it will happily deliver. "fast" is an interesting subject, as different cars, and different dongles, have different samplerates. OBDSim has a bunch of stuff built in for making the timing work right, including a few ELM optimisations.
As for what data in what format... it's an elm327. 90% of what I know about communicating with ELM devices I learned from the ELM327 datasheet. I honestly recommend that you try it. Grab that datasheet. Start up obdsim. Using putty, or hyperterminal, or some COM-port-communicating-thing-of-your-choice [I use PuTTY], and get started. It's a human-interactible protocol. There's an explanation of what you want to do here; but instead of "OBDII tool of your choice", you want "PuTTY".