Plumbing and electricity are pretty easy to do yourself. The library or a knowledgeable friend is all you need to get an understanding.
If there's any chance you'll want electricity and/or indoor plumbing, be sure to lay some 4 inch (or bigger) pipes through the width of the wall or foundation for the wires and the water pipes to run through.
You'll need a water intake and a drain outlet. These can be put at the bottom of the foundation (for buried wire and pipes) or through the foundation.
If you bury the pipes between the foundation stones, make sure the stones are not leaning on the pipe but onto other stones. If you live where it freezes, the water pipes will need protection from the frost where they are exposed to the outside air. Angle the pipes for the plumbing slightly down towards the outside, so that if a leak develops, it'll run out. (See wiring section on page 99.)
You can put the access pipes on top of the foundation and cob them in place. The wiring and plumbing is usually pretty ugly so you may want to put them lower in the foundation so they will be less obvious.
Any extra space between the access pipe and the plumbing pipe or electric wire can be filled later with cob or plaster.
Firewood box in the foundation
Some folks put a firewood box opening through the foundation. The box can be filled from the outside so you won't have to carry firewood in through the house. Make the foundation extra deep if you want the foundation to be continuous.