I'd be cautious about feeding that much milk to an 8-day old calf... even a holstein. Sounds like a potential scour problem.
To that I say especially a holstein.
As far as water... I rarely provide that until weaning (around 6-8 weeks).
Water is crucial, in my opinion. There were holstein calf raisers around here that thought too much water caused scours. Yeah, too much water in the milk replacer, maybe. When they withheld water, their death rate didn't go down...it went up. Of course, this is Texas. Maybe the climate played a part in it.
I'll start offering grain around 1-2 weeks of age, but it usually takes a few weeks before they start eating it well. Wouldn't worry about him not being too interested in anything but milk at this age.
Offering calf starter grower right off the get go...no later than 3 days...is also crucial, at least around here. When the babies start to drink water and eat grain, the incidence of scours goes way, way down. Again, this is Texas...Stephenville, Texas. I'm only going by what I observed and what I was told by the Holstein calf raisers.
FWIW, the blender sounds like a good idea. I generally use a bucket and whisk to mix it thoroughly; ain't no way anyone can mix 2 cups of milk replacer and 4 pints of water in one 4 pint bottle without having half of it stuck to the bottom. :lol:
Oh, honey, ain't that the truth!