Probably. No, make that 'definitely'. A small mixer like
this probably wouldn't be money wasted either. You could plug the midi/audio interface into the board, then the board into the PA for the audience and also into an amp for you and the rest of the band to have onstage monitoring.
If I sound like I'm kinda slugging in the dark on this one, I am. I've been on homerecording.com for more than a year now and you're the first person who WANTS to bring their computer onstage not to sequence anything but to use a soft synth. Most shy away from the very thought of bringing a computer to a gig and I think it's mighty brave of you to want to do it...
There are a whole bunch of free soft synths
here, not to replace your minimoog but to add to it. Do a search on your platform and the word 'free'. Some are good, some great, some mediocre but they're all free.
If you're asking how it's best to map the controllers on the Radium, I'd start by putting the filter cutoff and the filter emphasis (resonance) on faders 1 and 2, then the attack, decay and sustain for the filter on 3, 4 and 5 and the loudness contour modifiers - attack, decay and sustain - on 6, 7 and 8. Use the main data entry to control the master volume. Then set the top row of knobs the three oscilator levels and the noise level with the bottom row set for arpeggiator on/off and speed and LFO rate and waveform.
This is just a suggestion and YMMV (your mileage may vary), but that's what I would use as a starting point. And don't be afraid of 'ruining' a patch (sound) by twisting those knobs and tweaking those faders. The original Minimoog had no memories at all - the manual included patch sheets to be copied and when you got a sound you liked you had to write it on the patch sheets with a pen or pencil.