In terms of sequencing, I'm of the opinion that there's no sequencer more powerful than a DAW. This does create the problem of getting accurate timing to the modular system, but this is resolved with an audio interface that has ADAT out and a handful of Expert Sleepers modules (an ES-3, and ES-5 and an ESX-8GT gets you 8 CV and 16 trigger/gate outs.) However, if you're looking to break away from the computer there's a wide variety of sequencers you can use as well (I'll leave that to the experts).
As for drum modules, I was screwing around with designs and I cooked this dream system up:
The first row is what a system built around "standard-oriented" modules would look like. It's all Tiptop 808/909 drum style modules. It is not at all adventurous when it comes to design, but it does get you plenty of drum horsepower.
The second row is more of a "designer-oriented" drum rig (with the exception of the mixers on the right, which are meant for mixing it all together). It's a quad AD envelope generator, two oscillators, a multi-type noise source, a filter, a waveshaper and a quad-VCA. You could create a single quite complex drum sound, or 3 or 4 simple drum sounds out of this setup.
This could be condensed down by using smaller, simpler oscillators. Also, the waveshaper and filter aren't really completely necessary but they help and give you more options. Once condensed, the module arrangement could be repeated a few times (sans the noise source...you really only need one noise source but you may want a few multiples).
So those are the opinions of somebody who is relatively new to modular on drum synths.