re: Boston in late July

Book a lunch reservation at the Castle Hill Inn in Newport RI outside on the lawn for food and drinks
The views are spectacular!

I assume you will have a rental car to get around Rhode Island if coming from Boston, they have a big parking lot by The Breakers Mansion and you can tour whatever mansions you want and you can walk the Cliff Walk around pretty much all of them with awesome views.

As far as Boston, plenty of things to do and Abita's post has a lot of info and good recommendations for food and drink.
We love the Italian North End and can't go wrong wherever you end up eating and go to Mike's Pastries or one of the other desert shops.
The Prudential Center has an Eataly and great for shopping as Newbury Street is close by.
Last time we went to Concord Lexington which isn't far from Boston and did the tour and sightseeing. It was a neat little side trip I had never done before and see where the first shots were fired in the Revolutionary War.