Can I have a funeral/memorial Mass said for a loved one whose body has been cremated, even though I don't have the cemetery arrangement finalized?
The ideal form of Christian burial is according to the Church's liturgy, and the statements of the American bishops is the burial of the intact body. But if cremation is used, then the next best form is to have the funeral with the intact body and then have the cremation and the depositing of the ashes later.
You are always free to have a Mass for your dear departed with or without the body or ashes. If the ashes are not yet going to be deposited for practical reasons, then you should have the Mass without them, just a memorial Mass. Then, when the ashes are able to be deposited, you should have a priest or deacon bless them and deposit them at the Catholic cemetery you choose.
It is not permitted for the faithful to keep the ashes of their dead indefinitely in their homes; they must be buried or placed in a niche in a Catholic cemetery, or at least in a blessed plot or niche in a non-Catholic cemetery if for a good reason the Catholic cemetery is not being used.