Honestly, I think you need to chill a bit. If you're septic is truly a concern for you, look up a septic company and discuss your concerns with them, have them check it out.

Same advice for the foundation! (Except finding the appropriate contractor for the job, the septic guy probably won't be too helpful with that)

Something to consider: homeownership can be stressful, for sure. If you consistently worry about all the "what ifs" you'll never enjoy actually living in it. You should be thankful you were able to actually buy a house (I'm sure many of us would love to be capable of owning). There's always a possibility that shit will happen, that's life.