This is the simplest way to get started:
(a) right-click in the TCP area below any existing tracks,
(b) select "Insert virtual instrument on new track",
(c) select the VSTi,
(d) click [Yes] on the "Build Routing confirmation" window; that will create tracks for all of the audio outputs from the VSTi.
Now you will have the VSTi track sending MIDI to the VSTi and several tracks for the audio outputs from the VSTi.
Within the VSTi, load your instruments and set the routing for each one - sending its audio to a particular audio output pair; depending on the VSTi you may need to do some additional configuration work within the VSTi itself (e.g. to create / enable the output channels).
Back in Reaper, name the audio tracks for the drum kit pieces. Colour the tracks as you wish. SAVE them all as a Track Template.
Have a look at
signal paths for Kontakt 4, SampleTank and ...