How difficult are colts and stallions?

If you like the colt, get it but geld it. Colts and stallions are a pain in the because you have to have separate locations for pasture turnout etc. You have to be careful what they are stabled next to etc. As they get older and the testosterone kicks in, they will start displaying more dominant behavior and can become quite a handful which can make them difficult to train and handle. Some bloodlines produce notoriously bad minded horses and with the testosterone influence too, they can become quite aggressive and even dangerous. There is already a overpopulation of horses in this country and unless this was some outstanding prospect that you had intentions of showing/racing/jumping etc with an intent to eventually stand as a stallion prospect, I'd bguy him if you thought he was the right horse and then get him cut ASAP.