For rhythm patterns, you should look into the drum machine (rhythm generator), not the arpeggiator. It's activated from the pads.
Any recommendations (i.e., PC vs. Mac)?
Mac in general is a much, much better choice. They are not just computers, it's more of having a great experience in getting your ideas implemented with high levels of speed and pleasure. Equipped with all you need out of the box, much more easy to use in every way, much more reliably day to day, and - finally - falling in love with a Mac is no bad thing.
You can also look into our computers section, there are quite a few people that switched to a Mac in the recent years and never looked back. Seriously, these are amazing machines no matter who you are and how you look at it.