Hey RG, a 1RU line mixer with a stereo send is the go but then $s... The little mixer you have in mind will work but limits your options a bit.Don't know why you want a pedal in front, I thought that's what you wanted to get away from, I know I did, although IIRC you like a bit of boost before your MP1.
I'd go Guitar > MP1 > Mixer >amp for Fx, MP1 send > Fx > Mixer. Run Fx full wet but change the volumes (delay, reverb etc) within the Fx patch. So this way the Fx are applied to the MP1 sound and your wet dry mix is done with the mixer vols, so set it with Fx off, then turn them up at the mixer to taste (you need to adjust the mixer levels for your loudest patch so it doesn't overload the channel, then all softer patches will be fine). Think of it like a PA mix where you add a little delay and reverb to the vocal channel (or any other channel) via you outboard Fx unit(s) which take their input from a Fx send and return back down 2 channels and get mixed in. If you want different amounts of specific Fx, make a patch in the Fx unit exactly how you want it. And if you want the same MP1 patch but with different Fx, make copies of the MP1 patch, or if you want the same Fx patch on multiple MP1 patches (as is what I do), midi map them either in the MP1 midi map or the Fx midi map. Eg I use the same mild delay and reverb (QV 000) for most of my patches, so I edited the Quadverb midi map to map the desired MP2 patches (110, 111, 112, 113) to be 000 in the QV.
So I run Guitar > MP2 > mixer ch 1 & 2 (panned L/R), Fx send 1 & 2 > Quadverb L/R in, Fx send 3 > IPS33 in (I no longer bother with the distortion loop), Quadverb L/R outs > Mixer ch 3 & 4, IPS33 A/B outs > Mixer chan 5 & 6 (and turn up ch 5 & 6 Fx send 1 & 2 (so IPS33 output is also sent to Quadverb)) Mixer out L/R > amp > cab(s).If I had a 1 RU line mixer with a stereo Fx send, I run it the same except take the MP1/2 loop send to feed the IPS33.