A right royal milestone! As if saying “I do” to Prince Harry in front of 2 billion viewers on May 19 weren’t enough, Meghan Markle dove headfirst into life as HRH. Just three days later, she attended her first engagement as the newly minted Duchess of Sussex, trotting out the Queen Elizabeth-approved pantyhose. Since then, the former Suits star’s life has been a whirlwind of events, trips and family obligations — with, luckily, plenty of R&R away from the fray of London on the $5.4 million estate she and her husband, 33, rented in the Cotswolds, a 90-minute drive from the city. Now, at summer’s end, the fashion icon, 37, and Harry are preparing for their first overseas tour to New Zealand, Fiji, Tonga and Australia — the site of…