Well a Devils Own #3 is 370ml/min, much more than Joey will be running, and there is zero reason to run straight meth on the OBDII 1FZ. Mostly water like 30% meth to 70% water would be a better mix since the enthalpy of water (40660 J/mol) is higher than methanol (35200 J/mol). You do not spray meth injection on an OBDII truck for fuel enrichment you are only using it for charge cooling. This is different than the people using the methanol as a fuel source.
I don't know how many mL. I use devil's own nozzles. They start at #1 and go up from their. #1 being the smallest I use #3. So its not a very big nozzle. If Im doing a lot of mountain driving then I will go through a gallon in about 10 to 14 days. If Im just putzin around town a gallon will last me a month. My motor is a 3.4, so naturally it should use less meth than a 4.5. If you have room to hide one somewhere, a 3 or 4 gallon tank would be nice. If you have access to a dyno, you can fine tune the meth nozzle size. Devils own also sells a ramp up controller thats not very expensive so you can increase the meth as boost increases which looks like a cool option. Also, keep in mind that if you run 100% meth, and you use your washer jug for meth and cleaning the windshield, I noticed that it oxidizes the clearcoat on the paint near the washer nozzles. I normally run 50% and its fine. It also de-ices the windshield nicely. But with a dedicated tank you can run 100% as an option without worry if you want.