Nope, Ronin's quite right here. Eurorack isn't the right thing for basic pads and the like. First of all, pads get you into the polyphonic end of the pool, and that's one area where Eurorack (or any other modular system) gets VERY spendy. You would need...
1) at least two VCOs per voice
2) a VCF per voice
3) a VCA per voice
4) a mixer module that can handle this properly
5) a polyphonic MIDI controller and a Eurorack MIDI interface that supports your needed voice count
6) all of the other stuff you'd need in the cab to support this.
Potentially, a few thousand dollars AT BEST for a very simple modular poly. Compare this with something like a Modal Argon 8, which comes in at $750 street and which is a far more capable polysynth than anything you could concoct in Eurorack without spending close to $10k or worse. Unless you have this sort of cash laying around in a collection of laundry hampers and bushel baskets, this isn't your best solution. Oh...and the space for this honker, too. Can't forget that...
A better solution for you, since you're clearly more accustomed to the software environment, would be VCV Rack. In it, you can actually assemble a modular polysynth (IF you have enough speed and processor capability!) and see what I'm talking about here. And ultimately, you're probably best tinkering with this QUITE a bit before pulling the trigger on any hardware; know your problem before trying to solve it!