There are a lot of choices here. What is the size/thickness of the casting? Is there a specific tensile strength called out. What capabilities/requirements are there for PWHT? Any tougness/hardness/or other special requirements? Do you have a filler metal in mind or one that you are required to use? Answers to all of these questions would get a more specific or applicable answer.
Generally though, use a preaheat of 400-600 F depending on casting thickness, filler, etc. If you know the tensile strength requirement for the casting, us a matching filler such as 11018, 12018, or 14018. PWHT is generally required, and can range from below 900 to over 1200F depending on properties required. (Unless specifications call for full heat treatment (Normalize, quench, and temper) for PWHT, and then it's a whole different ball game). In non-critical applications, some people just wrap the part in an insulating blanket to slow cool, and use it without PWHT, but it is not normally recommended.