The trouble with rockets is that they carried their own oxygen instead of using air. The engine it self was light (very attractive) but the fuel was heavy. The two chamber rocket for the Me 163C weighed 365lbs, a single chamber rocket was lighter.
Unfortunately it consumed fuel at the rate of 19.5lbs of C stoff per lb of thrust per hour and an traditional 40.1 lbs of oxidiser (t-stoff) per lb of thrust per hour, this compares to a Jumo 004 consuming 1.4lbs of fuel per lb of thrust per hour.
That consumption seems impossibly high if you apply that to the 3,800 lbf thrust and 7.5 minute full throttle endurance of the Me 163. That would be 3775 lbs (1714 kg) of combined fuel+oxidizer consumed per minute and 28310 lbs (12853 kg) of total fuel/oxidizer. Your figures seem to be off by a factor of nearly 3:1. Wiki lists the combined fuel/oxidizer consumption at full throttle to be 20 lb/lbf/hr (combined fuel+oxidizer) which complies with the 7.5 minute figure and approximate 4 tonnes of fuel+oxidizer onboard.
Still about 14x poorer than the 004, but gives a good deal more margin for the thrust/weight threshold. And comparing a mixed powered aircraft using a single 004B and single 3,800 lbf rocket would offer nearly as much maximum thrust as 3x 004Bs (or better, but I'm going by the 1984 lbf offered by the 004B-4) and given the dry engine weights of perhaps 150 kg for the rocket engine and 719 kg for each of the jets, that's 869 kg to 2157 kg or some 1288 kg of additional fuel weight before the jets become more attractive for take-off/max thrust. (albeit you gain much more general advantages even before that point) Or the same difference for 2x 004s vs a single rocket engine. (enough fuel for about 2 min 14 seconds of full power thrust)
Though that said, with the amount of fuel the Me 163 carried, and its take-off weight, a similarly small aircraft with 2 jet engines (003s would be better, but 004s should have been possible) should have been better performing in most respects and much more fuel efficient. However, it would perform worse on power-out landings given the Me 163 expanded much more of its mass as fuel and thus glided better.
OTOH, using jet assist purely for take-off/climb would make much more sense given you'd only use a limited amount of fuel and expend all of that weight before entering combat. Something the Me 163's size with a single 004B and single 3,800 lbf jet might make a lot of sense, or slightly bigger than the 163 to properly accommodate the added bulk of the engine and weight increase. (me 262 with a rocket in the tail and drop tanks carrying the rocket fuel, might make sense, but a single engine jet with rocket assist might be more cost effective)
Good engine-out performance is critical for anything using those early jets with reliability issues, and in a single engine aircraft that means good dead-stick performance. (I'm not sure if the Me 163's landing skid arrangement would have made emergency landings on rough airfields or off airfields any more practical or less damaging than belly landings -obviously the Me 262 was poorly suited to belly landings given the underwing nacelles, taking that into account for a jet/mixed powered 163-a-like could have been significant -aside from trying a dorsal/saddle mount, embedding the engine in the fuselage above or below the rocket engine might have worked, above probably better due to potential of dripping corrosive rocket propellant during priming; an arrangement that allowed fairly quick engine replacement would still be necessary though, so a fairly easily removable 'embedded' module type arrangement would have been preferable -probably simpler than removing the entire long tail section as on the Mig 15 and P-80)
If the V2 really need 30 tons of potatoes (?) to produce the alcohol element of it's fuel I think dumping that project would have been essential!
Fermentation of ethanol really isn't all that efficient, if they'd really wanted to mass produce alcohol fuels efficiently, synthetic fuel plants would be the ideal option. Be it methanol, ethanol or other alcohols (methanol is the simplest/cheapest by far but has a lower energy density -at least part of the Me 163's high fuel consumption rate was due to the use of methanol and large portions of water in the fuel and oxidizer, the hydrazine isn't that efficient of a fuel either, and ethanol isn't THAT much better than methanol -plus methanol was seriously considered for use in the V2 and vaporizes more easily).
Small, relatively simple (nothing like the massive, costly hydrogenation synthetic fuel plants primarily used in war-time Germany) Fischer–Tropsch synthesis plants, including ones on the countryside closely associated with farms (potentially producing biomass feedstock both from crops and especially from waste -dry agricultural waste would be ideal as like wet brown coal or peat, wet plant matter has to be dried or heated to drive off the water before conversion to synthesis gas).
Wood works well as biomass feedstock for such factories too and along with a number of other plant materials, also produces some useful distillates directly from destructive distallation, including limited portions of methanol (hence 'wood alcohol' ) and wood tar, plus turpentine from pines. (the usefulness of that all depends on the region, and in the specific discussion on rocket fuel, wood alcohol and synthetic methanol production would be the relevant ones -stuff like turpentine in diesel or gasoline or alternative fuel blends is another topic)
That said, the V2 was hugely expensive and of limited practical use for a number of reasons, even ignoring the research costs, deployment aside from maybe a few special cases would be hugely costly compared to more conventional alternatives, including that synthetic fuel (or potatoes or grain) going to better uses elsewhere.
Hell, even for purse research use, the V2 was hugely expensive, and US testing quickly shifted to lower cost alternatives after running through their initial supply of captured V2s. Putting more of the V2's resources into SAM development with the Wasserfall program might have been more sensible use for similar resources. (engineering talent included) But, of course, that would mean greater interest in DEFENSIVE weapons development. (or possibly tactical short range offensive weapons too for potential short range SAS missiles -I wonder if a scaled down, tactical short range version of the V1 might have been useful too, something much easier to set up using mobile launch sites -pulse jets scale down really well, but the guidance system would be more problematic)
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