How should you address an odontoma (benign tumor)?

Remove it. In general, these should be removed. They can continue to grow and can damage or cause other teeth to shift. This is a benign tumor but it should be removed.
Depends on location. A definitive diagnosis of an odontoma can only be established after removal, but x-rays can give a good indication. Often, an odontoma is preventing eruption of teeth and it that case it should be removed as soon as possible. Often it is removed just to make sure it is benign. If there are no symptoms and periodic x-rays are unchanged for multiple years it is reasonable to continue observation.