A pretty sounding and low-hp module is the 2hp pluck.
It's 4 note polyphonic, has an interesting range of tones, and leaves you lots of rack room.
They are always a pain to tune because of the fiddly knobs and 2hp stuff is kinda cheap because they're cheap.
More than three 2hp modules in a rack is rarely worth suffering with their fit and control.

But... feeding it into mavis' external in can make for some astonishingly beautiful arpeggios.
Two plucks together is also nice. For tonal variety, add a 2hp bell.
The 3 together have provided me some "wow" moments where you have to just stop, listen, and smile.
cornishe_excerpt This is Pamela's Pro Workout -> A-156 QNT ->PluckPluckBell + Mavis into a Monsoon to stereo out.

Add a Doepfer A-138 narrow mixer to corral them, or you could add a Doepfer A-138s mini stereo mixer.
You'll also need a mult of some sort. The Doepfer A-182-1 stitchable mult
works great for this, adds 6hp more, and so now with pluck/pluck/bell/mixer/mult, we're still only
at 16 hp added and you've got lots of added fun.

I only wish that someone would make a unified PluckPluckBell with less twitchy tuning.