Regarding Chile, in the Puerto Montt area you have lots of beautiful options. You can go to Puerto Varas, Frutillar, Lago todos los Santos (Petrohue and Peulla), hike in Cochamo or visit Chiloe island. Considering you have just 4 days I would not go to the city of Puerto Montt and, clearly, choose some of the options I gave you.
While in Santiago, you should go to the city of Valparaiso and spend 1 night there. 2 nights in santiago is fine, and if you dont like big cities, you can hike in the Andes near santiago (cerro manquehue is the easiest, but there are others like cerro pochoco or cerro el Plomo).
I hope this helps.