You know...
While I don't have an mpc yet, I know a lot about how sequencers and midi work. I think you'll get a better grasp of the mpc sequencers capabilities knowing that the 300k/100k figures are for midi *events*, for example note on and note off. Counting only note on/off, you'd get 50.000 notes in the mpc1000 as each note on requires a note off. That's a lot, but we're not there yet; most (popular) music is repetetive with recurring themes and sections, or patterns in sequencer-speak. Most of the time there is no need to store each of these sections as separate entities, you simply tell the sequencer to repeat sequence A and B, X times in an A-A-B-A succesion for example. A song!
So, in a "does this make alot of importance in hip hop based beats?" kind-a-context, a 100.000 events is plenty.
However. Modulation, pitchbend, fader and slider movements generate a lot of events. Likewise if you want to embed synth patch data, in the form of system exclusive messages, so your external gear is set up with the right sounds for the song. Still, looking at it from a practical view, a little preparation goes a long way. You can quantize fader/modulation movements for example, reducing the resolution (number of events) of the movements. Most gear have plenty of patch storage meaning instead of storing patches in the mpc seq/song, you'd simply call them up from the mpc with program change messages, which are a whole lot slimmer than system exclusive chunks. Keep in mind that midi/sequencer data in turn is quite skinny compared to sample data. Which means that (live performance in mind) with the mpc1000 sample ram maxed out, you could load all of the samples for a set in one go and then if required load different seq/songs as the set progresses, minimizing the time between songs.