Seems like you have an idea on how to continue, but I just wanted to add that I had a similar problem when I first started rockscaping. The best way to learn is to study the attempts of others.
Slopes is best in my opinion to create a rocky affect but you can achieve a similar result just using bricks. Check out this mountain
I built using this idea.
When using slopes try to use a variety to achieve a natural affect. I'm a big fan of using 1x2, 1x3, 2x2x2, and 2x2x3 slopes to create non uniformity throughout your landscaping. Cheese slopes work great too for covering stray studs. Check out this micro castle
or this shrine
I personally try to steer away from burps as they tend to have the same rock pattern, which looks a little odd and uniformed when grouped together. Burps work great for internal structural support though. This is my personal opinion though, and I have seen many burp landscapes that look great in their own right.
Hope that helps, but check out more creations from different builders, everyone has a slightly different approach.