Good catch, it’s not just the VESC this presents a problem with but nearly every controller I’ve tried (RC, EV, eBike, etc) over the last 10 years.
The technical issues of long cables in general is two fold… first the long wires as already explained will increase the impedance or resistance of the length thus dropping the voltage and / or heating up so basically it’s a garden hose but it’s too thin to flow enough power to your pressure washer (in this case the ESC)… the capacitors help on the battery side because they allow the ESC to deliver transient bursts and they prevent or help to prevent the real killer of ESCs on long cable runs, the build up of eddy currents.
Now as far as sensor cables (hall sensor, ntm35 thermal or thermistor), while temperature and “variable” level signals may be attenuated or lose some amplitude over a long cable run, hall sensors are straight up 3 Parallel Bits or just on and off… since they swing is 0v to 4.7-5v it’s very unlikely there would be an issue introduced.
There are a ton of issues I’m skipping here, common sense rules here: Keep all wires as short as possible while being serviceable, use sufficient gauge and quality silicone or ptfe jacketed low resistance wire for power and phase (I use something like 24g silicone for my signal lines just for thermal and short resistance and flexibility, it really doesn’t matter as long as the wire you use here won’t fracture with vibrations),
Combine them sure… I head to my auto parts shop and get carbon fiber looking conduit tube… I pass all 6 wires from the enclosure contained in a single cable which splits to a Y within the truck area and each 3 phase side is then passed to the motor in another, thinner conduit tube - I’ve seen guys use 5/8, 1/4 and 1/8’ auto hot rod hose wrapping for effect but you can’t combine the phases - two motors, two controllers, 6 phases and 3 each (plus sensors).
Samsung Q30 is 15A maximum continuous discharge in 1P and 3000mah if memory serves, so it’s not a matter of can that pack handle the dual 63xx series BLDCs it surely can as 7P it will be 21AH and capable of 5C discharge continuous or 5 * 21 = 105 Amps Continuous, I’m not sure the peak discharge rate but this is fine… now your voltage is only 37v nominal and while you don’t specify your motor kV … I’m guessing around 190kv so currently the motor can spin up to 37v * 190 = 7030 RPM (this is not 100% accurate since it would be at 100% efficiency, think more like 85% loaded efficiency and that would be 7030 * .85 = 6022.25 RPM actual. Moving to the 12S would up your maximum motor RPM to 44.4v * 190 = 8436 RPM or at 85% efficiency 7170.6 RPM.
In addition to the higher RPM which obviously translates to higher top speed and likely faster acceleration it also means more power to some extent… again pulling from thin air, VESC x 2 @ 45A Each Continuous / 100A @ 15 second peak current so your power will go from 37v * 45 Amps * 2 ESCs = 3330 watts continuous power and 37v * 200 A = 7400 watts peak or surge to 44.4 * 45 * 2 = 3996 watts constant (nearly a full HP, 666w constant power upgrade) and burst power of 8880 watts (2 FULL HP MORE PEAK POWER).
To sort speed, if you presently on 10S have a “top speed” (assumes 83mm wheels and 16:36t gearing) of 6022.25 RPM / 336 * 83mm||3.27" / 2.25:1(36t:16t) = 26 TOP SPEED and going to 12S would in theory give you: 7170 RPM / 336 * 83mm}}3.27" / 2.25 : 1(36t:16t) = 31 MPH TOP SPEED
Now even though the 10s7p is fine, if you can go to 12s for a reasonable fee… do so, the system will run cooler and more efficiently (or can).
I listed the math to calculate speeds, rpm and no-load or loaded kV and RPM to expect so you can adjust to fit your numbers and build.
If I may offer one bit of advice, while yes some in the community have reinvented the wheel… don’t, if you stick with a somewhat “standardized” layout with the ESCs located nearest to the motors as possible and the battery other side then keeping your wiring short, neat and efficient should be super easy.
Hope it helps!