Can a man name someone else in his will to inherit his estate instead of his spouse?

Anyone can disinherit anybody they please. However, spouses in most states have special rights under law, sometimes even allowing access to trust funds set up for others. These laws were set up to protect widows whose husbands left everything to their mistress, although they have many other applications today. Best to meet with a local attorney to find out how best to carry out your wishes.

Yes and yes. Under Iowa law a spouse can receive nothing under a will, but it does not end there. The law provides a surviving spouse the option to elect against the will. Usually this allows them to receive one-third of the estate, but that can vary. If the spouses entered into a valid agreement prior to marriage it is possible to waive the right to elect against the will. There are some circumstances in which the pre-marital agreement may not be fully enforced. A consultation with an experienced probate and/or family law attorney is advised.

While I am not an attorney in IA and cannot speak specifically to IA law, the right of a spouse to "elect against" a will is common in all states to my knowledge.