Hi Lesley,
Not on your trip have to wait until October but have been to the States many times so will answer questions best i can.
I have an American adapter and not yet found anywhere it doesn't work, you should be fine.
Never needed insect repellent although southern texas was dodgy, rattle snake anti-venum is a must (only joking).
About $80 per day average if breakfast included ($20 lunch, $10 coffee/cake, $50 evening meal, drinks, entertainment, etc)
think some nights/excurrsions meals are included so can work that out and reduce accordingly, figure maybe slightly high but also covers stuff like bottled water and other consumables.
plus money for presents/souveniers.
plus money for optional excurrsions that are not pre-paid.
Tipping is around 15 to 20% but check your bills some places include it in service charge. The service is excellent in America as they always have plenty of staff who are paid very little or nothing and tips are their salary.
And remember americans advertise the pre-tax price so the bill is sometimes more than you expect.