hey great choice to pick it up, you won't be disappointed.
couple of things I would highly recommend -
1. watch all the video tutorials - they really show you the ins and outs of the instrument.
2. pay special attention to the tutorial on edit groups - this is a very, very powerful feature of rmx and really is a key component for unlocking its true potential
3. check out the sage expanders by spectrasonics and ilio's - they rock (I know as I own them all

4. check out recycle from propellerheads. I use this program to cut up just about everything i can get my hands on and import it into RMX
5. remember to think outside the box - I use RMX for all manners of sounds - drums, bass, guitars, soundscapes etc. There really isn't any limitation on what you can run through the instrument.
have fun and let me know if you have any questions