Dobermans have been our breed since 1997 or so. They have ranged in weight from 80#s to 110#s. Ziggy weighs 5#s plus a little something. He is our first dog of any other breed (besides our cats, Clyde and Mustache, who were well over 15#s). Luckily, I am a dog trainer, so I am very familiar with the special problems of smaller breed dogs.
Small dogs are awesome and need training just like large dogs to reach their potential. However, there are special considerations that go into owning and caring for a small dog.
First of all, they can be hurt by any number of things if you are not careful. They just do not have the bulk or strength to withstand things many other dogs can. On the other hand, you don't want them lacking in confidence, adventure, or socialization. Small dogs, like Ziggy, can also easily be carried away by predators (birds of prey, coyotes, other dogs, a cat could even get Ziggy!). We are sure that playmates are trained, and that they are supervised in order to play with him carefully. The rule here with large dogs is that the smaller dog is always right, and if they are not, I will intervene and they do not need to. It is very important that the large dogs here know that it is never okay to go after the small dogs. (also not okay to go after the large dogs here, but there is an additional level of protection needed for toy breeds)
Non social behaviors that can reduce the patience level of the pack are not allowed from the small dogs either. A bad behavior exhibited towards another has the potential to erode the relationship until something tragic or unfortunate happens. Therefore, even though small dogs are usually less than 20#s, it is also important that they are trained and supervised. While toy breeds can not do much damage to a medium to large dog, their behavior can incite a reaction from them that could have serious if not fatal consequences. However, when rules exist, this keeps that possibility at a minimum.
Another thing we need to be careful, is that there is water that Ziggy can get to. Our large dogs drink from pails of water. Ziggy can get up there, but if the water is not high enough, he can not reach it. So we are sure to bring him aside several times a day for his own water time, unless we have seen that he has reached the larger pail and gotten his water (and same for any toy breed guests that come here).
Going to a dog park or the beach means looking out for my little guy. I don't coddle him, but I am on the lookout for potential problems to avoid. To some dogs that have not been socialized with small dogs, Ziggy is fair game to chase like prey. Being a dog owner means always being aware of my surroundings anyway (as I don't want my large breed dogs to be attacked either), but it is especially important to be aware of what is going on around Ziggy.
Extreme weather especially the cold is a problem for most toy breeds. They just do not have the insulation to keep themselves very warm. Even when you have a coat on them, sometimes it is just too cold for them to spend any real time outdoors in the winter.
Tooth decay happens in toy breeds, and it can happen when they are fairly young! This is a lot different than larger breed dogs. It is thought this happens as they do not chew enough on bones. Be sure to consider a solid dental routine for your small breed dog, and get their teeth checked out at each health check veterinarian appointment.
Toy breeds also have their advantages of course. Picking them up is very easy when they are injured, to take out of a situation, and to walk around in stores that let you do that. Travelling with small breed dogs is much easier on just about any level. Feeding smaller breed dogs is obviously cheaper. The vaccination and other such health expenses (besides surgery as toy breeds actually need specialists sometimes) are cheaper. Exercising a smaller breed dog is easier. They live longer, and are easier to take care of during their old age. Also if they make an accident in the house, it is only so big . Toy breeds are much easier to pick up after.
Just be aware of these other items:)