The tightening sequence is in this PDF file - see page 6:

http://www.w124performance.com/service/w124CD1/Program/Engine/602_603/01-5800hx.pdf

The head bolts can be re-used if they are within spec. ALthough they are a torque-to-yield design, as long as they aren't stretched, they're fine. It doesn't hurt to replace them but not everyone wants to shell out ~$60 for new bolts. The spec is also on page 6 of the above factory procedure... basically, up to 2mm stretch is allowed, more than that and the need replacement.