1) "Should I just take the train from CT to Como and stay there?"
Most people posting here do not choose to focus their Lake Como experience on the town of Como itself, but instead in or near the mid-lake destinations of Varenna, Menaggio, or Bellagio. The town of Como is not especially representative of the "Lake Como" experience you see in Rick Steves' videos and books; nothing wrong with the town, it's pleasant, but some mistakenly equate "Lake Como" with the Town of Como, an easy mistake to make.
2) "I would like to take a boat around the lake. Are they fairly expensive?"
No, most people take the public ferries, which are affordable. Many choose to use the public ferries to cruise between the 3 mid-lake towns mentioned above--these are where the "postcard" views are that you've probably seen.
3) "Should I make Milan my base and take a morning train there and back?"
That's one option that some choose. But others enjoy sleeping in one of the mid-lake villages. For only a one night visit, there are trade-offs either way. Just don't sleep in the town of Como, not necessary. Either Milan or one of the mid-lake destinations.
