This question seems to be all over the place now, but I'll try to address all concerns.
First, about horses and houses: The capital cities for each major hold (Whiterun, Windhelm, Riften, Solitude, Markarth) have both a house available for purchase and a stable. The stables are located just outside the main city, and horses are always available for purchase at a price of 1,000 gp. In order to purchase a house in the city, you are generally required to complete a quest for the Jarl, or another task of great significance to the hold.
Horses come in many colors but, with only two exceptions, are all the same in regards to vital statistics such as speed, stamina, and health. The two exceptional cases are not purchasable at stables - they are quest rewards. Frost is faster than normal horses. Shadowmere has much higher health, regenerates health more quickly, and re-spawns a few weeks after death. All the rest of the horses are generic, and none of the horses can be customized. If you want a horse of a certain color, just shop around.
As of 2/28/2012, there is no in-game method provided by Bethesda (out-of-the-box, or via expansions/mods) to armor your horse. There may be console commands or other hacks that can do this, but I don't consider those "in-game". Some third-party mods may enable this functionality, but those would only currently be available for PC and are not "official".
Houses come in varying sizes and prices. All of the player-purchasable houses can be enhanced with certain modifications that add decor, storage containers, or other useful items. The enhancements which are available, and their prices, vary between houses. When you buy a house, you are given a "Home Decorating Guide" specific to that house which lists all the available upgrades but does not include pricing. You can find out the prices by going to purchase the upgrades.
All house enhancements must be purchased from the Jarl's steward in the same hold, who can usually be found in the Jarl's palace.