If your question is whether you should wait to file your request for entry of default (against the defendant who has not appeared) until after you have filed your 1st amended complaint, then yes--wait. This way, you would avoid having to (very likely) re-serve the defendant who has not appeared in the case. Hope this makes sense.
Many factors are involved. You should at least consult with an attorney.
You don't say whether the fraud matter includes the defendant who has not appeared. If not, you can take a default now. But, should that defendant try to have it set aside later on, you will have more chance at making it stick if you show that you gave ample warning that you would request a default if no answer were filed.
If you are going to file a new complaint, you should do it now, before the demurrer hearing. Otherwise, you will have to seek the court's leave to amend. If you do file an amended complaint, you will have to re-serve the defendant who has not answered before you can take a default.
You can file an amended complaint in response to the demurrer.
If the amendments have nothing to do with the defaulting defendant, then go ahead and default him now.