Is it dangerous to have cvs or amniocentesis?

No. This is a personal decision. The risk of losing a pregnancy because of cvs is about 1/100. The risk of losing a pregnancy because of an amnio is 1/500.
No. It is uncommon to have complications from amniocentesis or cvs. There is a small increased risk for miscarriage from these procedures. The physician who is performing the procedure can give their rates, usually less than 1% for an amniocentesis and 1% for cvs. The acog website has a nice handout on these procedures.