Keep in mind the reason that most people use a contractor that will look after the whole job is because they don't really know what needs to be done. If the contractor has all the people and equipment to do the job, he may have people that can do more than one of those jobs but he has to charge enough to pay for equipment that isn't used ever day. More often he will have people that do the core work and sub out the rest. The advantage of haver a plan to start with is that you can cut up the job and get quotes on all parts of the job. A back hoe to prep the trench look after drainage and back fill when done. Any framer, most construction labourer or carpenter can build forms and pore the footings. Then you need a brick layer. All of these people are the sub contractors that the general contractor use and they will have time between jobs for work like this. The down side of doing it like this you may have to deal with 20 or 30 people to get all the quotes and then the job may take a little long as not everyone will be available on your time line. If it is just a matter of saving money???