If you're fond of working this way as I am, you really should check out a couple of excellent step sequencer plugins, ERA and EST here:
www.sonicbytes.com
ERA is the MIDI version, EST is the sampler version. There's per note sliders for note length, note delay, fills etc...you can even enter a chord into a single step, or switch to a drums mode. It's a really focused, creative way to work, and IMO they're way superior to both Stepchild and Reason's Matrix.