Like many apparently simple jobs, when you get into the details of right and wrong, a sprinkler system can present many problems for a novice. You have already found some of them. My advice is to make a scale drawing of your property, get all of the details on water supply you can, and find a professional irrigation company who will give you the information you need, provide the proper materials, and even give you a cost for installation. You might be surprised how affordable they can be. Even if you DIY it, you will have the information to do it right. A number of years ago, a local company designed my system at no cost. They only required that I buy my materials from them. It was a pleasant surprise to find that there cost for materials was actually less that the Big Box Store! Twenty six years later, the original sprinklers are still working just fine.