Press F4 or go to the Window menu and choose Show On-screen Piano Keys and you'll get a virtual keyboard that fires MIDI towards the currently selected device in the Rack. It has two modes : Mouse and Computer Keys. In Mouse mode you can trigger virtual piano keys with the mouse and there are repeat and hold options. The green area above lets you set an octave range. Switch to Computer Keys mode and specific keys are mapped to MIDI notes, with octave control and sustain shortcuts also available. You can manually enter a velocity value or specify automatic variation from light to heavy to have Reason translate your basic key presses into more believable parts. You can customize assignments in the Preferences > Advanced section.
More than two in fact. If you drag new modules over to the right-hand edge of the Rack rather than down below, they are created alongside the existing column. Look out for a white right-facing arrow to indicate that this is going to happen. You can keep going too, adding a third, fourth or fifth column of instruments. It makes no difference to the routing, but if you're on a widescreen monitor it can make it easier to scroll left and right rather than up and down. You might even want to group modules into separate racks: all drums in one, synths in another and so on.
The cabling system is really powerful but you don't always want to see them. With larger projects they can really start to obscure your view of the back of the Rack. In the Preferences > General section, you'll find cable display settings. These include an option to only show cables for the currently selected device, only show cables for devices you have manually routed and to hide all cables. You can even suspend cable animation here!
Reason analyzes all imported or recorded audio for tempo information and adds slice markers. By double-clicking on any clip, you can view and edit these markers and also bounce them into a Dr Octo REX for re-sequencing. From this same contextual menu you can also choose to slice any audio clip at its slice markers. If you do this, you get lots of small audio clips which you can move around or export individually.
If you go to the File menu you'll see an option called Song Information. This lets you add metadata to a song file which people will see if you share the song file'"just like in the Reason demo songs. You can embed an image (256x256 pixel JPEG) and add text and web links as well as an email address. It's a good way to make sure anyone opening your song file can find out more about you.