I do something similar with my Helix. I run isolated paths for my guitar and keyboard for live gigs.
Running multiple paths alone does not put a significant load on DSP. It is only when you add effect and amp blocks that you start consuming bits of DSP. In my Helix presets, my guitar processing is configured with one amp block and around 10 effect blocks across three sub-path in series, although my only always-on effect is a compressor or an overdrive. I switch on the other effects as needed using the footswitches. Then my keyboard processing is configured with a volume pedal, a few effects, and sometimes an amp block across one sub-path, with the effect and amp blocks only enabled by footswitches. Both paths can be stereo, but my preference is to mix the final outputs down to mono. I have never run out of DSP.
Helix (including LT) has three mono 1/4-inch analog inputs: guitar, return 1, and return 2 that you can use for your guitar, bass, and Moog. Each one can have an isolated processing path.
Helix (including LT) has four analog outputs: left and right XLR and left and right 1/4-inch, each of which can be used by separate paths (or a mix of paths). For your configuration, you would probably use a pair of left/right outputs for your stereo guitar, and one left output for your mono bass and one right output for your mono Moog.
My guitar and keyboard paths go to two separate XLR outputs for the PA. For my own on-stage monitoring, I mix them together when I bring a powered PA speaker, and I keep them separate when using a Powercab Plus (and use the digital output for my guitar path).
There are a couple of things to note. Every one of your Helix presets needs to have multiple paths so that when you change presets all your sources have paths to the outputs. Once you get your first preset working the way you want, you can use it as a template and copy it as a starting point for new presets.
When you select a preset, everything will change to the new preset. I keep the keyboard path in my presets almost identical, and only change the guitar effects and amp in each preset. In each of my presets, I use the exact same three footswitches for my three most commonly used functions: switching from compressor to overdrive, setting amp drive level low or high, and switching the guitar output from normal to high. All my other footswitches are used to turn effects on and off, which are different in each preset. The expression pedal is initially a volume pedal for my keyboard path, and pressing the toe switch enables the wah effect and changes the expression pedal into a wah pedal.
You will enjoy having and almost endless selection of high-quality effect and amp models available for all your instruments while only having to use one multi-effect unit. The massive reduction in signal and power cables compared to a pedal board makes setup faster and the whole rig more reliable.
Let us know how it works out for you.