Although you don't need the feats you do need the level. You can start adding abilities to an amulet/holy symbol at 3rd but would have to wait until 5th to add abilities to the warhammer and 7th for a ring.
Taking the warhammer as your bonded item does mean you start with a free masterwork weapon, but since you are multi-classing I would opt for the amulet, and see if the nice DM will let you use Cleric spells as well as Wizard ones to enhance it.
Taking the warhammer as your bonded item does mean you start with a free masterwork weapon, but since you are multi-classing I would opt for the amulet, and see if the nice DM will let you use Cleric spells as well as Wizard ones to enhance it.