If input is set to all>Omni, you can have all your controllers set to the same VST, so in a way, it's the default. I have the Korg NanoKey, but ants ate it, and only half the keys work. So I know I can have a NanoKey and NanoPad on the go at the same time. But The Editor programme give me the impression it would only see one of each type. I'm not sure, but the way it says show connected devices, makes it look like it could only show one of each type. This had me searching. I found users using the Nanopad for Tractor, and they were having issues with two and having to mess with things to get it to work.
For drums, each part if the kit has more different hits types assign to different keys, Ad2 has about 8 octaves worth. The Hi-hat for instance has 12 hit placements and foot positions. Not that I use all, but a hi hat line often uses at least 3-4 to create realism, but having them all available (well typically 8) helps me find the combination I'm looking for. I often focus to just two parts of the kit at the same time when I play, then add in another layer. So I a Hi-Hat run, then a snare and bass drum run. Or maybe snare and hats, get the bassline sorted and return to the bass drum later.
The bass drum is the only drum on Ad2 that have one hit, but I found that I like it assigned to two keys, so flames are easier to play. With the small pads, this is more so. I set up the pads so they are a mirror image of each for my left hand a right, so my hands don't have to too cross over. So if a snare has two of the same hits assigned to two different keys, I assign on to the right hand and one to the left. My current default pad lay out has a row of 8 hi-hat articulations, and then a row with two kicks in the middle, a snare of each type either side, a rack tom of each type either side and a floor tom of each type assigned to the outside.
So I know I would like at least 32 pads
Cymbals row
Toms row
Hi hats row
Snare and kick drum row.
As you know I am a lover of Insert Piz Mini Cords, for inputting cords from a single key, and lean towards seventh cords and Jazz Voicings. I assign a cord to say C, then the C above has an inversion, or a different voicing, and then again for the C above that. Then I repeat for each degree of the scale.
With an 8 x 8 pad, I'd assign a c to the first column, with ascending in octaves up the rows, then d, e, etc ending on c again. This would give me 8 variations on a c cord, with just a triad, an inversion of a triad, and open voicing of a triad (dropped 2) then seventh cords, with open and closed voicings and inversions. (or maybe leave the bottom row to be an octave on single notes in the bass range, with cords above it, so I can accompany the chords with different movements in the bass.