For most Honda B series gearboxes you will require around 2.5 litres. Almost all K-Series transmissions require 2 litres, please check your specific transmission's fluid capacity to ensure the correct number of bottles are ordered. For example, an Accord CL9 gearbox can take around 2.2 litres if being rebuilt and dry assembled. EP3 and FN2 are typically around 1.9L on overhaul.
In almost all circumstances MTF-3 is the best choice for your Honda gearbox. Dependant on model, Honda's service schedule states the fluid should be replaced anywhere from 50-75,000 miles in a standard road-going car, however as a best practice to keep your transmission performing at its best in a performance-orientated Honda, we'd recommend replacing every 25,000 miles or 2 years regardless of mileage.
Fresh transmission fluid is also required whenever drained for the fitment of a clutch, flywheel, differential or new bearings and seals.
Most LSD manufacturers recommend only using your vehicle manufacturer's recommended oil with their products, some like manufacturer's like MFactory have a specific oil recommendation, in their case Torco. We're sure they have their reasons, but will state many of our customers choose MTF3 regardless with great results.
For those more technically inclined and as a point of comparison, MTF-3 is a GL-4 specification oil with 75w-80 viscosity.