The small cracks you find in your foundation may be serious problems, requiring major surgery to head off a disaster. On the other hand, they may only be minor flaws requiring a patch job to remedy. Then there are the bulges that go unnoticed by the average homeowner until deep spider web cracks appear and water starts running through. What your situation is can only be determined by a trained professional. Having a survey done before you purchase a home can save you serious money in the long run, from shingles to basement.
If your foundation fails, the consequences can be major inside your home. So it is well worth the few extra dollars spent, to save you potentially tens of thousands within a year or two. Don't be shy about following along and asking questions while the survey is done either. Yearly inspections are the key to catching a problem while it's a minor one. Otherwise, it may blossom into something costing you the equity in your home. A professional inspection should still be done about every ten years.
If you already have problems with your foundation, you need to call a licensed home surveyor or city building inspector to get a handle on it. With this knowledge, you can weed out potential problem contractors who disagree with the diagnosis of the problem. Always ask to see your potential contractors' license. You can find out if your state requires one by calling your city's building inspectors office. Also, ask to see your contractors' insurance, and several references for this same project. Don't try and save money doing any work yourself. Rely on the professionals and you'll sleep better at night.
Any disruption to your life should be minor for average projects, although major problems mean major disruptions. Remember to include landscaping in your contract, and leave everything up to the professionals.