Hi Jana. I like young people who look to earn a few pence themselves rather than hold their hand out to their parents all the time. However, loving dogs is not an adequate qualification for handling dogs. To confidently perform the tasks you are planning you need to get some hands-on experience on handling different dogs and learn to recognise the signs of canine intention.
When you perform a service for reward you are responsible for any damage done to the dogs (fighting etc) and other people, animals and property due to your inability to properly control the dogs.
Have you thought about volunteering your time to a local kennel for a while? Make sure it is a reputable kennel rather than a dog factory. You might even end up doing the walking for that kennel for a small recompence. It is also an excellent way to get recommendations for dog sitting.
Reputable kennels are often willing to help genuine dog people, even when they don't profit from that.