[rotrex]

I would suggest you use a different architecture
Set of petrol fuel injectors at the OEM install location for petrol
2nd set of methanol compatible fuel injectors further up the intake runner or pre turbo fed by a methanol compatible fuel pump with a pressure regulater and return line into a small fuel cell, say 10l. Essentially a second fuel system. This way you get all the flow you want with the control you want. This has been done before and it works great.

Use your current water injection system to spray any water you need or want on top of that. As flow requeirements are now much reduced, use your current system as is. You may add 15% methanol to the water tank to keep it sterile.

There is no need to inject methanol and water at once as a mix. It has its merits, but I would not try to build a classic water injection system with membrane pumps to provide the entire fueling of a car. There are suitable and reliable pumps,fuel lines, connectors, fuel pressure regulators and injectors on the market for just that. Fuel injectors will also give you the precise metering capability out need for the same money as 4 water/meth valves and jets. They are plug and play to any ECU with 2nd injector bank capability such as the Emerald K3 I am using. Hondata will likely support this as well.

Besides methanol those pumps, injectors etc. would also be E85 compatible if you shall have the desire to try it. It is more stable than pure methanol and available at petrol stations. You could also run a mix of e85 and methanol. You gain flexibility.

Run petrol off boost and it automatically switches to e85/methanol, 100% ethanol etc. as you wish. Water comes on top of this from the system you already have. If you go that far, do it right.