I've run whiterock may times.
I have always put in at buckman. there is a major risk of bad things happening to your car there if you leave it. it all just depends on who is partying out there. usually the put in is littered with glass and shotgun shells. maybe it will just be some hippies, but maybe not. i have a secret spot i park at after unloading about a half mile away that seems much safer, although i have left a car at the put in overnight a few times without problems. I wouldn't reccomend it though.
it's doable in a day, but as everyone has said the wind coming out of the canyon into coshitty can be really really awful in the afternoon. it's better to do the majority of the stretch in one day and camp close to the lake, and do the outgoing paddle in the morning while the wind is still non-existant.
kayaks and canoes are fine, and rafts will be ok at higher water, but the end of the river is so silt laden it can be a big trouble if you choose the wrong channel. paddling/rowing a raft across the lake, wind or no wind, seems like a huge pain though.
only a few notable rapids, ripples mostly, fun with lots of flatwater in between. but at 5000 cfs like it hit last year, the ancho canyon rapid can be nasty...III+. sand can create standing waves where there was flat water the season before, so it can get hairy for the inexperienced, especially in canoes.
its a great stretch, but keep your eyes on the ground when you get out and walk. I have never seen more rattlesnakes anywhere on earth, especially in NM.
Also, the feral cows aren't a problem, but the feral bulls can be. I got chased into the river while trying to scout the big rapid by a big big angry bull.
high water makes scouting/camping a bit more difficult as well as the beaches are gone. also, as said, always camp river left, its just better and no worries about rangers, who you almost certainly wouldn't see anyways.
there is a ton of wildlife on the trip, and the canyon is gorgeous. nobody really paddles there much except the occasional fish hugger, so it is really nicely secluded.
this is understandable because for the type of stretch it is, the long shuttle and the lack of major whitewater, it just isn't that profitable an attraction.
also, if you take beer for the last section, make sure the rangers at the boat ramp don't see it. booze is a no no at coshitty, and they will cite you if they see you with alcohol, i have seen them check coolers and such before.
i really recommend this trip, it is serene and beautiful, and not busy at all.