From the link I provided above:
Chocolate should never be melted with very small amounts of liquid. The amount of liquid added must be at least 25% of the chocolate. For chocolate with 55 to 60% cacao, you'd need 1 tablespoon liquid for every 2 ounces chocolate. High-percentage chocolates (60 to 70%) need more liquid, 1 1/2 tablespoons per 2 ounces. This prevents the dry particles (cocoa and sugar) in the chocolate from binding together and becoming lumpy.
Cold liquids should never be added to melted chocolate, as they can cause the chocolate to seize. Instead, ensure that your liquids are warm (but not boiling) when you add them to chocolate.
I don't think it matters if you add the chocolate to the cream or the cream to the chocolate. Start with everything at room temperature. Heat the cream but don't heat it too much. You don't mention how many ounces (grams) of chocolate you have and how much cream you are talking about.
Does the amount of white chocolate and cream seem right--as mentioned above, the amount of liquid is at least 25% the amount of chocolate? I personally would add all the cream at one time.
How hot should the cream be? Not boiling. Not room temperature. It should feel quite warm to the touch, your body temperature is 98 degrees F, boiling is 212 degrees F (or about that), it should be some where in between. I'd aim for about 150 degrees F.
ETA: RPCookin says to use a much lower temperature for the cream. I'd use a warmer cream if the amount of cream is about 25% of the amount of chocolate. The chocolate will be at room temperature, say 70 degrees and it is about 3-4 times the amount of cream. The cream's temperature with the chocolate's temperature, in the end, needs to be about 100 degrees F to 110 degrees F.