Can't comment on #1 other than that you generally want to cook grass-fed beef rare or medium rare, not more than that. Not sure about an aftertaste... it will taste different than grain-fed though.
2) It depends on the vendor. I'm buying from a guy who does low-volume and we had to find people to split the whole cow... so one guy is getting a half, and then another family and my husband/I are splitting the other half (they don't do 1/4s, so you have to split it up yourself).
Those prices seem reasonable but if you shop around you might find something cheaper... and the weights seem around right too.
I've read 100 pounds for a 1/4 cow before, but the cow I'm getting is a lot bigger and our 1/4 will be 150ish pounds. Depends on the cow.