Hi,
I personally use an Ibanez CCL Analog Chorus and an Alesis Nanoverb with the Minibrute. Both work fine and sound nice (Nanoverb) to fantastic (CCL Chorus). I am also an experienced guitar player with a large stompbox collection, and concerning output levels and impedance I'd like to contribute the following:
Modulation FX (phasers, flangers, chorus...) as well as reverb/delay FX won't stir up much trouble. They are best used in an FX loop anyway (i.e. when connected to a guitar amp), where output levels and impedance are not that different from a synth. Just use and enjoy them, and do not worry.
Amplifying FX (in particular, distortion and wah wah units) may be tricky since the output level of a synth can (but not necessarily is, you just have to try it) be a bit high for them. Being a bit careful with the gain knob (in overdrive/distortion pedals) is not a bad idea. Also, distortion pedals for bass (!) guitar are worth a try since they are designed for operation with the higher output levels of a bass guitar.
Also, be careful if your speaker setup includes tweeters. It is not a bad idea to make them switchable and turn them
off when playing a synth through a distortion unit. The keyboard player in a former band of mine some 20+ years ago just blew them within
under 5 seconds when he played some '
Deep Purple Distorted Hammond Organ Sound' using his DX7 with the distortion unit he borrowed from the second guitarist...