I went for the Helix rack with the foot controller.
Partly because I wanted to keep the brain away from the beer, but also for ease of use on a desk when recording. The floor unit is pretty big and would take up all my desk room! I already have a rack sitting there so it was an easy choice.
There's also the bending down to tweak stuff rather than having it at waist height. (Although you can actually tweak with your feet too - and the buttons are capacitive so you can touch them to see what is assigned to that switch and the settings without actually turning that button on or off)
The Rack and controller option does not have an expression pedal. I got the helix specific Mission L6H model to go with it. It plugs either into the brain, or into the footcontroller. I have mine into the foot controller with a couple of patch leads.
It allows the toe switch to also be programmed for things beyond just turning the wah on. My Cliff Burton Patch (For whom the bell tolls) uses it for the intro section - the toe switch turns on the wah, and a second fuzz stacked with another to get the completely nasty grating sound he had. When it's off, it is just a volume, when on, wah and fuzz.
IIRC the only physical addition the rack + controller has is that as a total it has another set of expression inputs compared to the floor unit- basically because the main one with toe switch is on both the brain and the controller.
If you run out of them, then the Source Audio Reflex expression / midi controller would solve the problem. That thing is amazing. I haven't got one as I don't need one, but friends have and they are controlling all manner of things with it. 2 wahs at the same time in reverse, while controlling speed of a phaser etc.
There is no Sub-Dub bass model on the Helix. At the moment there is the usual selection of SVTs. Mesa 400+, GK and others, but the EQ is very powerful. There are the amp EQs, then separate EQ blocks, and then global setting EQ as well. More bass models are in the next firmware update, due this month.
The individual settings for the EQ blocks and the Amp EQ can be set as "Snapshots" - so a footswitch can change the values of any or all of the EQ settings without changing a patch- therefore no patch loading time.
I'm biased because I bought a Helix, but the UI is amazing - so easy to use. It comes with a Beginners Guide info sheet, and the full instructions on a memory stick. I've never even looked at the stuff on the stick, I imagine that unless diving into MIDI it won't be needed by many people.