The keyboard node can be set to legato (monophonic) or 2, 4, 8 or 16 note polyphonic. The keyboard and MIDI modules in the library are a wrapper around the keyboard node. open them up and you can change the polyphony by clicking on the keyboard node. You can also change the MIDI channel from omni (any channel) to channel 1 though 16. When set to polyphonic mode, the keyboard node will generate a polyphonic output which will create multiple copies of whatever it is connected to, so somewhere in the signal path you need to use a poly to mono node to mix the signals back together. Watch your CPU usage, multiple copies of a complex oscillator, filter and envelope generator can quickly overwhelm the CPU.
This is great! I just wanted to chime in with a note about polyphony - you’ll want to maintain it throughout your chain for as long as it’s necessary for the sound/function, but then collapse it to mono before certain effects where it doesn’t matter that the effect is running in polyphony - for example, polyphonic distortion can sound good because it’s probably level-dependent and will be more expressive on each note you play, however, polyphonic delay or reverb isn’t - it will sound the same regardless of whether the signal is polyphonic or not. So what I did here was insert a PolyToMono node at a good point in the patch and shaved off 3-5%CPU usage just from that.