Hi PRB, welcome to the DHC forum.
The muzzleloader season - Sept. 21 - Oct. 4, 2009 is a time of change for weather in Kansas with cool fronts starting to come down about one a week or so and so its possible you could see warm sunny weather for days, perhaps a thunderstorm and nasty cool rainy weather all in your 1 week of hunting.
Expect winds out of the North or NE when its cooling down or raining and out of the South when its warming up, very seldom do you see West or East winds in Kansas and I do mean winds, we have lots of windy days and its very infrequent to have a completely calm day in the fall.
So if its clear and warm for most of your week you could see 70's-80's for highs but if you are there in a rainy cool spell with north winds it could be highs in the 50's-60's so my advice is to bring both warm and cool weather gear and maybe even rain gear in case you are forced to hunt in the wet to try to fill your tag but usually the rainy cool spells are short in duration that early in Oct. Expect the worst weather and hope for the best.
Northern Kansas tends to have slightly larger bodied whitetail deer than to the southern Kansas areas (SE Kansas generally has the smallest) and most kansas deer are grain fed as most of Kansas is crop and pasture land so we have big, fat, healthy deer with no winter kills. In Northern Kansas a buck that is only around 3yrs old can weigh around 180-200lbs here and 4-5 year bucks probably hit around 250lbs, so not as big as northern U.S. states but plenty big, our does are probably as big as the bucks down in Alabama.
As far as big racked bucks go you can see P&Y/B&C sized racks just about anywhere in Kansas and i've heard of good bucks in those units in Cloud county that you mentioned, there is no one county here that is a golden area like some states have like the famed 'Pike County Illinois', in Kansas a trophy buck or two can pop up from just about anywhere you deer hunt and they do.
As far as the land type - Mostly flat to gently rolling, lots of crop land and some pasture land (some light woods but don't worry about mountains or deep forests) LOL . You may or may not have strong tall trees for a tree stand depending on your friends land because in some areas only the drainages, creeks will have good trees near them so if you are driving up to Kansas I would bring a tree stand and a ground blind if you can unless they say they have stands or blinds already in place for you to use.
We've had more than average rain this summer so they have plenty to eat, they eat green winter wheat in the late fall-winter and corn, soybeans, grass, etc in the summer and they have places to hide and they know them like you know your living room.
If you are hunting drainages or shelterbelts with trees I would look for and hunt the trails you will find in them unless the friends family tells you where they see them every day.
Good Luck!
New Kansas state record whitetails over the last 10 years by county -
http://www.deerhuntingchat.com/viewtopi ... 0197#30197
http://www.kdwp.state.ks.us/news/Other- ... First-Buck