Instruo Harmonaig would tie those three oscillators nicely. An Expert Sleepers Disting (Mk4 or ES) is a great modular multi-tool. A Low Pass Gate like a Make Noise Optomix will give you different timbres than just using filters. A complex oscillator like DPO or CS-L can produce some great ring mod, AM/FM sounds. I personally love harmonic oscillators like the XAOC Odessa or the Verbos (my fave brand right now) modules and free running LFOs like Erica Synths Black Octasource or the DivKid Ochd.
It all really depends what sounds you want to sculpt though. There are infinite directions to go from here. Analog/digital/subtractive/additive/whatever
While outside FX are nice, I find it much easier to keep everything in the case, especially when there are really great modular solutions. A Mutable Instruments clone called Typhoon (Original MI Clouds firmware + the two alternate firmwares, Kammerl & Parasites), Make Noise Morphagene & ErbeVerb, Strymon Magneto (also a pedal tho) all come to mind and would add some nice depth to the case.