The lawn will look perfect on the tour. Ask about the wind rating, the caterer map, and the ordinance anyway.
Newport's caterer map is rigid, and worth memorizing before you fall for a room. Preservation Society mansions use a short caterers of choice roster; Glen Manor House and Mount Hope Farm are Russell Morin exclusives; Blithewold is Blackstone's; Castle Hill, the Longwood venues, and the hotels keep everything in-house. Mansions often need a full field kitchen built on site, which adds real cost, while state and town properties, Eisenhower House and the Rotunda among them, take any licensed caterer you hire.
Newport quiet hours start at 10pm, with limits of 65 dBA by day and 55 at night measured at the property line, and a minimum $300 fine after 11. Outdoor amplified music generally ends by 10pm, mansions wrap between 10 and 11, and Glen Manor closes its bar 30 minutes before an 11pm hard stop and requires a police detail. Get each venue's end time in writing, then plan the after party at a hotel that wants you there.
Tent season runs roughly May to October. Ask who owns the tent, what gust rating it carries, and whether sidewalls and heaters are included, then get the weather call time for fog and wind along with hurricane postponement terms. Solve transport last: mansion lots are modest, Ocean Drive is a two lane road 10 to 20 minutes from downtown, shuttles from the hotel districts are standard, and some historic gates cannot take a full size coach.