Actually, that sequencer complement isn't all that different from what I presently have (2 x BSP, SQ-1 [for my own MS-20], Keystep) in addition to the various incorporated ones in other synths. And yes, they all play very nicely with each other. My plan for later this year is to cap this off with a Koma Komplex and use that as a 'hub' for all of the other hardware sequencers + direct interfacing with my modular. This'll then free up a BSP to use as a drum sequencer for an ancient MXR Drum Computer which has a blown sequencer but which recently received a trigger-in 'fan' for this exact purpose.
VCOs aren't the whole problem with how VCOs sound, btw. Very pure VCOs tend to sound rather meh, so by putting some things inline with them that introduce some nonlinearities, you can beef their sound. Also, just one VCO is probably two fewer than you need, because you want some slight detunings and waveform nonsynchrony to get a more interesting sound. The whole key to the Minimoog sound is, in fact, these two things; not only do the VCOs have a tendency to drift slightly even when warmed up, the Minimoog also contains the guts of the CP3 mixer for mixing these...and the CP3 isn't a very clean mixer, but it's not clean in a musical sort of way, if that makes sense. Feed that on to the classic LPF on there, and that's "that sound".
As for effects...unless you want something non-replicated in outboard (such as Intellijel's Rainmaker), my suggestion would be to grab some cheap outboard devices and a 1/4" patchbay for them, then have fun routing all sorts of processing cascades, insert loops, etc.